Pathways

The steroid biosynthesis pathway occurs in the endoplasmic reticulum leads to the production of various sterols. In Arabidopsis thaliana, the major products are cholesterol, brassicasterol, stigmasterol, campesterol, and their derivatives. These products serve various roles including signalling and structural support. Stigmasterol is the principal sterol in with campesterol being second most abundant. The pathway begins with farnesyl pyrophosphate produced in the terpenoid backbone biosynthesis pathway. Squalene synthase catalyzes the reaction of two molecules of farnesyl pyrophosphate to form presqualene diphosphate and then squalene. Squalene is reduced by squalene monoxygenase to form 2,3-epoxysqualene. 2,3-epoxysqualene can be used to form cycloartenol via cycloartenol synthase. This leads to the primary path of steroid biosynthesis in Arabidopsis thaliana. Cycloartenol undergoes a series of reactions to form 24-methylenelophenol. 24-methylenelophenol can be converted to 24-ethylidenelophenol by 24-methylenesterol C-methyltransferase. 24-methylenelophenol and 24-ethylidenelophenol undergo similar separate reactions to form two different sterols. 24-methylenelophenol and 24-ethylidenelophenol are reduced by methylsterol monooxygenase 2 to episterol and δ7-avenasterol respectively. These are oxidized by delta(7)-sterol-C5(6)-desaturase to 5-dehydroepisterol and 5-dehydroavenasterol. These then undergo a series of reductions to form 24-methylenecholesterol and avenasterol; 24-epi-campesterol and β-sitosterol; and finally brassicasterol and stigmasterol. 24-methylenecholesterol may also be reduced by delta(24)-sterol reductase to form campesterol. Alternatively, lanosterol synthase can use 2,3-epoxysqualene to form lanosterol. Lanosterol is reduced by sterol-14-demethylase to form 4,4-dimethylcholesta-8,14,24-trienol and then by delta(14)-sterol reductase to form 4,4-dimethyl-5a-cholesta-8,24-dien-3-b-ol. 4,4-dimethyl-5a-cholesta-8,24-dien-3-b-ol then undergoes a series of reactions to for zymosterol. Zymosterol is converted into 5a-Cholest-8-en-3b-ol by delta(24)-sterol reductase, which is converted into lathosterol by 3-beta-hydroxysteroid-delta(8),delta(7)-isomerase, then into 7-dehydrocholesterol by 7-dehydrocholesterol reductase, then into cholesterol by 7-dehydrocholesterol reductase.

The biosynthesis of steroids begins with acetyl coa being turned into acetoacetyl through a acetoacetyl CoA thiolase. Acetoacetyl -CoA reacts with an acetyl-CoA and water through a 3-hydroxy 3-methylglutaryl coenzyme A synthase resulting in the release of coenzyme A, hydrogen ion and (S)-3-hydroxy-3-methylglutaryl-CoA. The latter compound reacts with NADPH and a hydrogen ion through a 3-hydroxy-3-methylglutaryl-coenzyme A resulting in the release of coenzyme A , NADP and mevalonate. Mevalonate is then phosphorylated through an ATP driven kinase mevalonate kinase resulting in the release of ADP, hydrogen ion and mevalonate 5-phosphate. The latter compound is phosphorylated through an ATP driven kinase, phosphomevalonate kinase resulting in the release of ADP and mevalonate diphosphate. This latter compound then reacts with an ATP driven mevalonate diphosphate decarboxylase resulting in the release of ADP, carbon dioxide, a phosphate and a isopentenyl diphosphate. The latter compound can be isomerized into dimethylallyl diphosphate or reacth with a dimethylallyl diphosphate to produce geranyl diphosphate. Geranyl diphosphate reacts with a isopentenyl through a farnesyl diphosphate synthase resulting in the release of diphosphate and farnesyl diphosphate. The latter compound reacts with hydrogen ion, NADPH through a squalene synthetase resulting in the release NADP, pyrophosphate and squalene. The latter compound reacts with hydrogen ion NADPH and oxygen through squalene monooxygenase resulting in the release of NADP, Water and (3S)-2,3-epoxy-2,3-dihydrosqualene. The latter compound reacts through a 2,3-oxidosqualene lanosterol cyclase resulting in the release of lanosterol. Lanosterol reacts with hydrogen ion, NADPH, and oxygen through a cytochrome P450 lanosterol 14a demethylase resulting in the release of formate, water, NADP and 14-demethyllanosterol. The latter compound reacts with hydrogen ion and NADPH through a c-14 sterol reductase resulting in the release of NADP and 4,4-dimethylzymosterol. The latter compound reacts with methylsterol monooxygenase resulting in the release of 4α-hydroxymethyl-4β-methyl-5α-cholesta-8,24-dien-3β-ol which reacts with methylsterol monooxygenase twice to obtain 4α-carboxy-4β-methyl-5α-cholesta-8,24-dien-3β-ol. The latter compound then reacts with an NADP C-3 sterol dehydrogenase resulting in the release of water, NADP and 3-dehydro-4-methylzymosterol. The latter compound then reacts with NADPH and a hydrogen ion through a 3-keto sterol reductase resulting in the release of NADP and 4alpha-methyl-zymosterol. The latter compound then reacts with a methylsterol monooxygenase 3 times, followed by one reaction with c-sterol dehydrogenase and one reaction with 3-keto sterol reductase resulting in the release of a zymosterol. The latter compound reacts with SAM through a sterol methyltransferase resulting in the release of s-adenosylhomocysteine and fecosterol. Fecosterol is isomerized into episterol. The latter compound reacts with c-5 sterol desaturase resulting in the release of ergosta-5,7,24(28)-trien-3β-ol which then reacts with a c-22 sterol desaturase resulting in the release of ergosta-5,7,22,24(28)-tetraen-3-β-ol. This latter compound then reacts with a C-24 sterol reductase resulting in the release of an ergosterol.

The biosynthesis of steroids begins with acetyl coa being turned into acetoacetyl through a acetoacetyl CoA thiolase. Acetoacetyl -CoA reacts with an acetyl-CoA and water through a 3-hydroxy 3-methylglutaryl coenzyme A synthase resulting in the release of coenzyme A, hydrogen ion and (S)-3-hydroxy-3-methylglutaryl-CoA. The latter compound reacts with NADPH and a hydrogen ion through a 3-hydroxy-3-methylglutaryl-coenzyme A resulting in the release of coenzyme A , NADP and mevalonate. Mevalonate is then phosphorylated through an ATP driven kinase mevalonate kinase resulting in the release of ADP, hydrogen ion and mevalonate 5-phosphate. The latter compound is phosphorylated through an ATP driven kinase, phosphomevalonate kinase resulting in the release of ADP and mevalonate diphosphate. This latter compound then reacts with an ATP driven mevalonate diphosphate decarboxylase resulting in the release of ADP, carbon dioxide, a phosphate and a isopentenyl diphosphate. The latter compound can be isomerized into dimethylallyl diphosphate or reacth with a dimethylallyl diphosphate to produce geranyl diphosphate. Geranyl diphosphate reacts with a isopentenyl through a farnesyl diphosphate synthase resulting in the release of diphosphate and farnesyl diphosphate. The latter compound reacts with hydrogen ion, NADPH through a squalene synthetase resulting in the release NADP, pyrophosphate and squalene. The latter compound reacts with hydrogen ion NADPH and oxygen through squalene monooxygenase resulting in the release of NADP, Water and (3S)-2,3-epoxy-2,3-dihydrosqualene. The latter compound reacts through a 2,3-oxidosqualene lanosterol cyclase resulting in the release of lanosterol. Lanosterol reacts with hydrogen ion, NADPH, and oxygen through a cytochrome P450 lanosterol 14a demethylase resulting in the release of formate, water, NADP and 14-demethyllanosterol. The latter compound reacts with hydrogen ion and NADPH through a c-14 sterol reductase resulting in the release of NADP and 4,4-dimethylzymosterol. The latter compound reacts with methylsterol monooxygenase resulting in the release of 4α-hydroxymethyl-4β-methyl-5α-cholesta-8,24-dien-3β-ol which reacts with methylsterol monooxygenase twice to obtain 4α-carboxy-4β-methyl-5α-cholesta-8,24-dien-3β-ol. The latter compound then reacts with an NADP C-3 sterol dehydrogenase resulting in the release of water, NADP and 3-dehydro-4-methylzymosterol. The latter compound then reacts with NADPH and a hydrogen ion through a 3-keto sterol reductase resulting in the release of NADP and 4alpha-methyl-zymosterol. The latter compound then reacts with a methylsterol monooxygenase 3 times, followed by one reaction with c-sterol dehydrogenase and one reaction with 3-keto sterol reductase resulting in the release of a zymosterol. The latter compound reacts with SAM through a sterol methyltransferase resulting in the release of s-adenosylhomocysteine and fecosterol. Fecosterol is isomerized into episterol. The latter compound reacts with c-5 sterol desaturase resulting in the release of ergosta-5,7,24(28)-trien-3β-ol which then reacts with a c-22 sterol desaturase resulting in the release of ergosta-5,7,22,24(28)-tetraen-3-β-ol. This latter compound then reacts with a C-24 sterol reductase resulting in the release of an ergosterol.

The biosynthesis of steroids begins with acetyl coa being turned into acetoacetyl through a acetoacetyl CoA thiolase. Acetoacetyl -CoA reacts with an acetyl-CoA and water through a 3-hydroxy 3-methylglutaryl coenzyme A synthase resulting in the release of coenzyme A, hydrogen ion and (S)-3-hydroxy-3-methylglutaryl-CoA. The latter compound reacts with NADPH and a hydrogen ion through a 3-hydroxy-3-methylglutaryl-coenzyme A resulting in the release of coenzyme A , NADP and mevalonate. Mevalonate is then phosphorylated through an ATP driven kinase mevalonate kinase resulting in the release of ADP, hydrogen ion and mevalonate 5-phosphate. The latter compound is phosphorylated through an ATP driven kinase, phosphomevalonate kinase resulting in the release of ADP and mevalonate diphosphate. This latter compound then reacts with an ATP driven mevalonate diphosphate decarboxylase resulting in the release of ADP, carbon dioxide, a phosphate and a isopentenyl diphosphate. The latter compound can be isomerized into dimethylallyl diphosphate or reacth with a dimethylallyl diphosphate to produce geranyl diphosphate. Geranyl diphosphate reacts with a isopentenyl through a farnesyl diphosphate synthase resulting in the release of diphosphate and farnesyl diphosphate. The latter compound reacts with hydrogen ion, NADPH through a squalene synthetase resulting in the release NADP, pyrophosphate and squalene. The latter compound reacts with hydrogen ion NADPH and oxygen through squalene monooxygenase resulting in the release of NADP, Water and (3S)-2,3-epoxy-2,3-dihydrosqualene. The latter compound reacts through a 2,3-oxidosqualene lanosterol cyclase resulting in the release of lanosterol. Lanosterol reacts with hydrogen ion, NADPH, and oxygen through a cytochrome P450 lanosterol 14a demethylase resulting in the release of formate, water, NADP and 14-demethyllanosterol. The latter compound reacts with hydrogen ion and NADPH through a c-14 sterol reductase resulting in the release of NADP and 4,4-dimethylzymosterol. The latter compound reacts with methylsterol monooxygenase resulting in the release of 4α-hydroxymethyl-4β-methyl-5α-cholesta-8,24-dien-3β-ol which reacts with methylsterol monooxygenase twice to obtain 4α-carboxy-4β-methyl-5α-cholesta-8,24-dien-3β-ol. The latter compound then reacts with an NADP C-3 sterol dehydrogenase resulting in the release of water, NADP and 3-dehydro-4-methylzymosterol. The latter compound then reacts with NADPH and a hydrogen ion through a 3-keto sterol reductase resulting in the release of NADP and 4alpha-methyl-zymosterol. The latter compound then reacts with a methylsterol monooxygenase 3 times, followed by one reaction with c-sterol dehydrogenase and one reaction with 3-keto sterol reductase resulting in the release of a zymosterol. The latter compound reacts with SAM through a sterol methyltransferase resulting in the release of s-adenosylhomocysteine and fecosterol. Fecosterol is isomerized into episterol. The latter compound reacts with c-5 sterol desaturase resulting in the release of ergosta-5,7,24(28)-trien-3β-ol which then reacts with a c-22 sterol desaturase resulting in the release of ergosta-5,7,22,24(28)-tetraen-3-β-ol. This latter compound then reacts with a C-24 sterol reductase resulting in the release of an ergosterol.

Steroidogenesis is a process that through the transformations of other steroids, produces a desired steroid. Some of these desired steroids include cortisol, corticoids, testosterone, estrogens, aldosterone and progesterone. To begin the synthesis of steroid hormones, cholesterol synthesizes a hormone called pregnenolone. This is done by cholesterol from the cytosol or lysosome being brought to the mitochondria and becoming fixed in the inner mitochondrial membrane. Once there, the cholesterol becomes pregnenolone through three reactions. The enzyme responsible for catalyzing all three reactions is CYP11A, a side chain cleavage enzyme. After being created, the pregnenolone enters the cytosol, where the cholesterol originated. Once in the cytosol, pregenolone synthesizes progesterone, using two reactions. These two reactions are both catalyzed by an enzyme called 3-beta-hydroxysteroid dehydrogenase/isomerase. The enzyme CYP21A2 then hydroxylates progesterone, which converts it to deoxycorticosterone. Deoxycorticosterone then undergoes three reactions catalyzed by CYP11B2 to become aldosterone. 17alpha-hydroxyprogesterone is created from pregnenolone by using 3-beta-hydroxysteroid dehydrogenase/isomerase. CYP21A2 then hydroxylates 17alpha-hydroxyprogesterone which results in the production of 11-deoxycortisol. CYP11B1 quickly converts 11-deoxycortisol to cortisol. Cortisol is an active steroid hormone, and its conversion to the inactive cortisone has been known to occur in various tissues, with increased conversion occurring in the liver. Pregnenolone is an important hormone as it is responsible for the beginning of the synthesis of many hormones not pictured in this pathway such as testosterone and estrogen. Cortisol receptors are found in almost every bodily cell, so this hormone affects a wide range of body functions. Some of these functions include metabolism regulation, inflammation reduction, regulating blood sugar levels and blood pressure, and helps with the formation of memories.

Steroidogenesis is a process that through the transformations of other steroids, produces a desired steroid. Some of these desired steroids include cortisol, corticoids, testosterone, estrogens, aldosterone and progesterone. To begin the synthesis of steroid hormones, cholesterol synthesizes a hormone called pregnenolone. This is done by cholesterol from the cytosol or lysosome being brought to the mitochondria and becoming fixed in the inner mitochondrial membrane. Once there, the cholesterol becomes pregnenolone through three reactions. The enzyme responsible for catalyzing all three reactions is CYP11A, a side chain cleavage enzyme. After being created, the pregnenolone enters the cytosol, where the cholesterol originated. Once in the cytosol, pregenolone synthesizes progesterone, using two reactions. These two reactions are both catalyzed by an enzyme called 3-beta-hydroxysteroid dehydrogenase/isomerase. The enzyme CYP21A2 then hydroxylates progesterone, which converts it to deoxycorticosterone. Deoxycorticosterone then undergoes three reactions catalyzed by CYP11B2 to become aldosterone. 17alpha-hydroxyprogesterone is created from pregnenolone by using 3-beta-hydroxysteroid dehydrogenase/isomerase. CYP21A2 then hydroxylates 17alpha-hydroxyprogesterone which results in the production of 11-deoxycortisol. CYP11B1 quickly converts 11-deoxycortisol to cortisol. Cortisol is an active steroid hormone, and its conversion to the inactive cortisone has been known to occur in various tissues, with increased conversion occurring in the liver. Pregnenolone is an important hormone as it is responsible for the beginning of the synthesis of many hormones not pictured in this pathway such as testosterone and estrogen. Cortisol receptors are found in almost every bodily cell, so this hormone affects a wide range of body functions. Some of these functions include metabolism regulation, inflammation reduction, regulating blood sugar levels and blood pressure, and helps with the formation of memories.

Steroidogenesis is a process that through the transformations of other steroids, produces a desired steroid. Some of these desired steroids include cortisol, corticoids, testosterone, estrogens, aldosterone and progesterone. To begin the synthesis of steroid hormones, cholesterol synthesizes a hormone called pregnenolone. This is done by cholesterol from the cytosol or lysosome being brought to the mitochondria and becoming fixed in the inner mitochondrial membrane. Once there, the cholesterol becomes pregnenolone through three reactions. The enzyme responsible for catalyzing all three reactions is CYP11A, a side chain cleavage enzyme. After being created, the pregnenolone enters the cytosol, where the cholesterol originated. Once in the cytosol, pregenolone synthesizes progesterone, using two reactions. These two reactions are both catalyzed by an enzyme called 3-beta-hydroxysteroid dehydrogenase/isomerase. The enzyme CYP21A2 then hydroxylates progesterone, which converts it to deoxycorticosterone. Deoxycorticosterone then undergoes three reactions catalyzed by CYP11B2 to become aldosterone. 17alpha-hydroxyprogesterone is created from pregnenolone by using 3-beta-hydroxysteroid dehydrogenase/isomerase. CYP21A2 then hydroxylates 17alpha-hydroxyprogesterone which results in the production of 11-deoxycortisol. CYP11B1 quickly converts 11-deoxycortisol to cortisol. Cortisol is an active steroid hormone, and its conversion to the inactive cortisone has been known to occur in various tissues, with increased conversion occurring in the liver. Pregnenolone is an important hormone as it is responsible for the beginning of the synthesis of many hormones not pictured in this pathway such as testosterone and estrogen. Cortisol receptors are found in almost every bodily cell, so this hormone affects a wide range of body functions. Some of these functions include metabolism regulation, inflammation reduction, regulating blood sugar levels and blood pressure, and helps with the formation of memories.

Steroidogenesis is a process that through the transformations of other steroids, produces a desired steroid. Some of these desired steroids include cortisol, corticoids, testosterone, estrogens, aldosterone and progesterone. To begin the synthesis of steroid hormones, cholesterol synthesizes a hormone called pregnenolone. This is done by cholesterol from the cytosol or lysosome being brought to the mitochondria and becoming fixed in the inner mitochondrial membrane. Once there, the cholesterol becomes pregnenolone through three reactions. The enzyme responsible for catalyzing all three reactions is CYP11A, a side chain cleavage enzyme. After being created, the pregnenolone enters the cytosol, where the cholesterol originated. Once in the cytosol, pregenolone synthesizes progesterone, using two reactions. These two reactions are both catalyzed by an enzyme called 3-beta-hydroxysteroid dehydrogenase/isomerase. The enzyme CYP21A2 then hydroxylates progesterone, which converts it to deoxycorticosterone. Deoxycorticosterone then undergoes three reactions catalyzed by CYP11B2 to become aldosterone. 17alpha-hydroxyprogesterone is created from pregnenolone by using 3-beta-hydroxysteroid dehydrogenase/isomerase. CYP21A2 then hydroxylates 17alpha-hydroxyprogesterone which results in the production of 11-deoxycortisol. CYP11B1 quickly converts 11-deoxycortisol to cortisol. Cortisol is an active steroid hormone, and its conversion to the inactive cortisone has been known to occur in various tissues, with increased conversion occurring in the liver. Pregnenolone is an important hormone as it is responsible for the beginning of the synthesis of many hormones not pictured in this pathway such as testosterone and estrogen. Cortisol receptors are found in almost every bodily cell, so this hormone affects a wide range of body functions. Some of these functions include metabolism regulation, inflammation reduction, regulating blood sugar levels and blood pressure, and helps with the formation of memories.