Exploring the activity of the enzyme 11ß-hydroxylase in the polycystic ovary syndrome.

Background Hyperandrogenemic polycystic ovary syndrome (PCOS) may have occult corticosteroidogenic enzyme abnormalities. The current study compares the activities of 11ß-hydroxylase between normoandrogenemic PCOS (NA-PCOS) and hyperandrogenemic PCOS (HA-PCOS) phenotypes. Materials and methods Anthropometric, and biochemical variables were compared between normal cycling women [n = 272] and those with PCOS [n = 453]; either normoandrogenemic [n = 98] or hyperandrogenemic [n = 355]. Univariate and multivariate logistic regression analyses were performed using 11ß-hydroxylase enzyme activity as the criterion variable. Results 11ß-Hydroxylase enzyme activity tended to be slightly higher in both PCOS subgroups and did not change with ethnicity. Using univariate logistic regression, 11ß-hydroxylase activity in controls was associated with dehydroepiandrosterone, insulin, homeostatic model for insulin resistance (HOMA-IR), and high-density lipoprotein cholesterol (HDL-C). In NA-PCOS women the activity of 11ß-hydroxylase was associated with estradiol (E2), androstenedione (A4), and androstenedione/dehydroepiandrosterone ratio; in the hyperandrogenemic (HA-PCOS) group, 11ß-hydroxylase activity associated with sex-hormone binding globulin (SHBG), 17-hydroxypregnenolone (17-OHPE), fasting glucose, and ß-cell activity. After multivariate logistic regression, androstenedione/dehydroepiandrosterone ratio, and ß-cell activity were the best predictors of 11ß-hydroxylase activity in controls; in NA-PCOS group only androstenedione/dehydroepiandrosterone ratio was confirmed as a significant predictor of 11ß-hydroxylase activity, and in HA-PCOS patients, 17-OHPE and ß-cell activity demonstrated to be significant predictors. Conclusions 11ß-Hydroxylase activity was equal in different ethnicities. The prevalence of decreased 11ß-hydroxylase activity was higher in the HA-PCOS phenotype. 17-OHPE, and ß-cell function are significant predictors of 11ß-hydroxylase activity in HA-PCOS subjects. These findings may help to identify which PCOS patient would have benefit in measuring 11-deoxycortisol (compound S) and 11ß-hydroxylase enzyme activity.

Role of genetic variation in regulation of aldosterone biosynthesis.

Aldosterone biosynthesis is not only altered in rare mendelian disorders. Recent evidence suggests that common polymorphisms in the genes mediating the final stages of aldosterone and cortisol production (CYP11B1 and CYP11B2 respectively) are also associated with milder alterations in adrenal corticosteroid biosynthesis. These abnormalities consist of a decrease in adrenal 11ß- hydroxylase activity and a subtle, life-long excess of aldosterone secretion which may lead to long-term cardiovascular risks. An interaction between the CYP11B1 and CYP11B2 genes may exist but is yet to be elucidated. This article describes the studies which highlight the importance of adrenal steroid synthesis in the development of hypertension and cardiovascular dysfunction as well as the role of common polymorphisms in adrenal synthetic genes in altering corticosteroid biosynthesis.

Functional consequences of seven novel mutations in the CYP11B1 gene: four mutations associated with nonclassic and three mutations causing classic 11{beta}-hydroxylase deficiency.

CONTEXT: Steroid 11beta-hydroxylase (CYP11B1) deficiency (11OHD) is the second most common form of congenital adrenal hyperplasia (CAH). Cases of nonclassic 11OHD are rare compared with the incidence of nonclassic 21-hydroxylase deficiency. OBJECTIVE: The aim of the study was to analyze the functional consequences of seven novel CYP11B1 mutations (p.M88I, p.W116G, p.P159L, p.A165D, p.K254_A259del, p.R366C, p.T401A) found in three patients with classic 11OHD, two patients with nonclassic 11OHD, and three heterozygous carriers for CYP11B1 mutations. METHODS: We conducted functional studies employing a COS7 cell in vitro expression system comparing wild-type (WT) and mutant CYP11B1 activity. Mutants were examined in a computational three-dimensional model of the CYP11B1 protein. RESULTS: All mutations (p.W116G, p.A165D, p.K254_A259del) found in patients with classic 11OHD have absent or very little 11beta-hydroxylase activity relative to WT. The mutations detected in patients with nonclassic 11OHD showed partial functional impairment, with one patient being homozygous (p.P159L; 25% of WT) and the other patient compound heterozygous for a novel mild p.M88I (40% of WT) and the known severe p.R383Q mutation. The two mutations detected in heterozygous carriers (p.R366C, p.T401A) also reduced CYP11B1 activity by 23 to 37%, respectively. CONCLUSION: Functional analysis results allow for the classification of novel CYP11B1 mutations as causative for classic and nonclassic 11OHD, respectively. Four partially inactivating mutations are predicted to result in nonclassic 11OHD. These findings double the number of mild CYP11B1 mutations previously described as associated with mild 11OHD. Our data are important to predict phenotypic expression and provide important information for clinical and genetic counseling in 11OHD.

Physiological and pathophysiological applications of sensitive ELISA methods for urinary deoxycorticosterone and corticosterone in rodents.

Deoxycorticosterone (DOC: a weak mineralocorticoid) is the precursor to corticosterone (B: the major glucocorticoid in rodents) and aldosterone (the major mineralocorticoid). The genes Cyp11b1 and Cyp11b2 that encode the enzymes responsible for DOC to B (11beta-hydroxylase) and DOC to aldosterone (aldosterone synthase) conversions are located on the same chromosome. The aim of this study was to develop sensitive and specific ELISA methods to quantify urinary DOC and B concentrations to assess the physiological and genetic control of the Cyp11b1/b2 locus. Antibodies raised in rabbits against DOC and B and horse radish peroxidase-goat anti-rabbit IgG enzyme tracer were used to develop the assays. Urine samples collected from mice held in metabolic cages were extracted with dichloromethane and reconstituted in assay buffer. The assays were validated for specificity, sensitivity, parallelism, accuracy and imprecision. Cross-reactivities with major interfering steroids were minimal: DOC assay (progesterone=0.735% and corticosterone=0.045%), and for B assay (aldosterone=0.14%, 11-dehydro-B=0.006%, cortisol=0.016% and DOC=0.04%) and minimum detection limit for DOC ELISA was 2.2 pg/mL (6.6 pmol/L), and for B ELISA was 6.2 pg/mL (17.9 pmol/L). The validity of urinary DOC and B ELISAs was confirmed by the excellent correlation between the results obtained before and after solvent extraction and HPLC (DOC ELISA: Y=1.092X-0.054, R(2)=0.988; B ELISA: Y=1.047X-0.226, R(2)=0.996). Accuracy studies, parallelism and imprecision data were determined and all found to be satisfactory. The methods were used in a series of metabolic cage studies which demonstrated that (i) females produce more DOC and corticosterone than males; (ii) DOC and corticosterone respond to ACTH treatment but not dietary sodium restriction; (iii) DOC:B ratios in Cyp11b1 null mice were >200-fold greater than wild type.

Studies on the origin of circulating 18-hydroxycortisol and 18-oxocortisol in normal human subjects.

18-Hydroxycortisol (18-OHF) and 18-oxocortisol (18-oxoF) are derivatives of cortisol found in primary aldosteronism but whose origin and regulation in normal subjects are uncertain. 18-OHF can be synthesized by zona fasciculata 11-beta hydroxylase; 18-oxoF can only be produced by zona glomerulosa aldosterone synthase (AS). Stably transfected cell lines expressing either CYP11B1 (11beta-hydroxylase) or CYP11B2 (AS) were incubated with cortisol and other substrates over a range of concentrations. Both enzymes could synthesize 18-OHF from cortisol, but only AS could synthesize 18-oxoF. AS was more efficient than 11beta-hydroxylase at 18-hydroxylation. The apparent Michaelis-Menten constant (K(m)) of AS for cortisol was estimated to be 2.6 microm. In five patients with adrenal insufficiency maintained on hydrocortisone, urinary free cortisol and cortisone levels were high; 18-oxoF was detectable in all patients and 18-OHF in three. It is likely that the 18-oxygenated steroids were synthesized from circulating cortisol, either in the zona glomerulosa or at extraadrenal sites. In eight male volunteers, dexamethasone treatment decreased urinary excretion rates of free cortisol, cortisone, 18-OHF, and 18-oxoF, confirming dependence of 18-oxygenated steroid levels on cortisol availability. In both groups, hydrocortisone administration resulted in detectable levels of 18-OHF and raised levels of 18-oxoF. There was close correlation between 18-oxoF and cortisol excretion during hydrocortisone administration in normal subjects (r = 0.86; P < 0.001). These data show, for the first time, that 18-OHF and 18-oxoF can be synthesized from circulating cortisol. The close correlation between 18-oxoF and cortisol suggests that 18-oxoF is normally produced by the action of AS using circulating cortisol as a substrate. Although 18OHF can be synthesized using circulating cortisol as substrate, our data suggest this is normally produced in the zona fasciculata by 11beta-hydroxylase from locally available cortisol.

Hypertension and adrenal disorders.

Adrenal disorders causing hypertension can be related to the dysfunction of either the adrenal cortex or the adrenal medulla. These disorders, including congenital adrenal hyperplasia (CAH), owing to 11B-hydroxylase deficiency and to 17alpha-hydroxylase deficiency; apparent mineralocorticoid excess; familial hyperaldosteronism type I; primary aldosteronism; Cushing's syndrome; and familial glucocorticoid resistance, primarily affect the adrenal cortex and cause low-renin hypertension. The classic disorder of the adrenal medulla resulting in hypertension is pheochromocytoma, although hypertension in obesity might also be associated with catecholamine secretion. In this review, we discuss these etiologies and the most recent advances in our knowledge of their pathophysiology, diagnosis, and treatment.

The human steroid hydroxylases CYP1B1 and CYP11B2.

Major advances have been made during the last decade in our understanding of adrenal steroid hormone biosynthesis. Two key players in these pathways are the human mitochondrial cytochrome P450 enzymes CYP11B1 and CYP11B2, which catalyze the final steps in the biosynthesis of cortisol and aldosterone. Using data from mutations found in patients suffering from steroid hormone-related diseases, from mutagenesis studies and from the construction of three-dimensional models of these enzymes, structural information could be deduced that provide a clue to the stereo- and regiospecific steroid hydroxylation reactions carried out by these enzymes. In this review, we summarize the current knowledge on the physiological function and the biochemistry of these enzymes. Furthermore, the pharmacological and toxicological importance of these steroid hydroxylases, the means for the identification of their potential inhibitors and possible biotechnological applications are discussed.

Amino acid residue 147 of human aldosterone synthase and 11beta-hydroxylase plays a key role in 11beta-hydroxylation.

A number of amino acids differ between aldosterone synthase and 11beta-hydroxylase. To assess their importance in determining the different functional specificities, we substituted aldosterone synthase-specific (aspartate D147, isoleucine I248, glutamine Q43, and threonine T493) with 11beta-hydroxylase-specific amino acids (glutamate E147, threonine T248, arginine R43, and methionine M493), respectively. I248T, Q43R, and T493M had no effect on steroid production compared to wild-type aldosterone synthase. However, CYP11B2-D147E caused a significant increase in corticosterone production and a smaller increase in aldosterone production from 11-deoxycorticosterone (DOC). This appeared to be predominantly due to an increase in the 11beta-hydroxylation of DOC to corticosterone mediated by a decrease in Km, which was 1.4 micromol/L for the mutant compared with 5 micromol/L for the wild-type enzyme. CYP11B2-D147E had no effect on the conversion of 11-deoxycortisol to cortisol. The reverse construct (CYP11B1-E147D), substituting the 11beta-hydroxylase residue with the aldosterone synthase equivalent, decreased the conversion of DOC to corticosterone, which was mediated by an increase in Km that was 7.5 micromol/L for the mutant compared with 2.5 micromol/L for the wild-type enzyme. Again, the conversion of 11-deoxycortisol to cortisol was unimpaired. Thus, amino acid 147 is involved in the transformation of the 17-deoxysubstrate, but not the 17alpha-hydroxysubstrate. The results demonstrate that a conservative change in amino acid, even at some linear distance from known active centers, can significantly affect enzyme substrate affinity and subsequent steroid hormone production.

Adrenal zonation: clues from 11beta-hydroxylase and aldosterone synthase.

Aldosterone and cortisol are the major mineralocorticoid and glucocorticoid produced by the human adrenal. Circulating levels of angiotensin II and potassium control the adrenal production of aldosterone, while the production of cortisol is controlled mainly by adrenocorticotropin. The capacity of the adrenal cortex to differentially produce aldosterone and cortisol relies to a large degree on the expression of aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1). CYP11B2 catalyzes the final steps in the biosynthesis of aldosterone and is expressed solely in the glomerulosa of the adrenal cortex, while CYP11B1 catalyzes the final steps in the biosynthesis of cortisol and is expressed in the fasciculata/reticularis. The zonal expression of these two isozymes appears to result from transcriptional regulation of the two genes. Herein, the recent progress in defining the cellular mechanisms that regulate transcription of these two isozymes and thus the capacity of the adrenal gland to differentially produce aldosterone and cortisol is discussed.

Interaction of CYP11B1 (cytochrome P-45011 beta) with CYP11A1 (cytochrome P-450scc) in COS-1 cells.

The interactions of CYP11B1 (cytochrome P-45011beta), CYP11B2 (cytochrome P-450aldo) and CYP11A1 (cytochrome P-450scc) were investigated by cotransfection of their cDNA into COS-1 cells. The effect of CYP11A1 on CYP11B isozymes was examined by studying the conversion of 11-deoxycorticosterone to corticosterone, 18-hydroxycorticosterone and aldosterone. It was shown that when human or bovine CYP11B1 and CYP11A1 were cotransfected they competed for the reducing equivalents from the limiting source contained in COS-1 cells; this resulted in a decrease of the CYP11B activities without changes in the product formation patterns. The competition of human CYP11A1 with human CYP11B1 and CYP11B2 could be diminished with excess expression of bovine adrenodoxin. However, the coexpression of bovine CYP11B1 and CYP11A1 in the presence of adrenodoxin resulted in a stimulation of 11beta-hydroxylation activity of CYP11B1 and in a decrease of the 18-hydroxycorticosterone and aldosterone formation. These results suggest that the interactions of CYP11A1 with CYP11B1 and CYP11B2 do not have an identical regulatory function in human and in bovine adrenal tissue.

Late steps of aldosterone biosynthesis: sheep are not rats.

1. The last three steps of aldosterone biosynthesis have been demonstrated to be catalysed by a single enzyme, referred to as CYP11B (or P450(11) beta) in cow, pig, sheep and bullfrog and as CYP11B2 (or P450aldo) in rat, human, mouse and hamster. 2. The related enzyme CYP11B1 (also referred to as P450(11) beta) in rat, human, mouse and hamster does not have aldosterone synthesis activity, but no such enzyme has been reported in the cow, pig or sheep to date. 3. Exclusive aldosterone secretion in the zona glomerulosa (ZG) of the adrenal cortex in species such as rat, human, mouse and hamster could be ascribed to the restricted distribution of CYP11B2 to the same region in the adrenal cortex. 4. In other species, such as cow, pig and sheep, the CYP11B enzyme is expressed throughout the adrenal cortex and, thus, the exclusive aldosterone biosynthesis in the ZG could not be explained simply by the distribution of the enzyme. 5. We have shown in the sheep that potassium loading and acute sodium depletion stimulate the CYP11B transcript levels, which are not further increased by chronic sodium depletion. 6. The predominant CYP11B in the sheep adrenal cortex catalyses the synthesis of aldosterone from deoxycorticosterone (DOC) in vitro, is expressed throughout the adrenal cortex and the corresponding transcript levels are increased by K+ loading or sodium depletion. In short, as far as the last step of aldosterone biosynthesis is concerned, sheep are different from rats. In the rat, the CYP11B2 transcript or protein is elevated by K+ loading or sodium depletion, but not the CYP11B1 transcript or protein. 7. We propose that during severe sodium deficiency there is a switch in the aldosterone pathway to one preferentially involving 18-OH-DOC and not corticosterone.

Structure-function relationships of aldosterone synthase and 11 beta-hydroxylase enzymes: implications for human hypertension.

1. The genes encoding aldosterone synthase (CYP11B2) and 11 beta-hydroxylase (CYP11B1) are very similar at the nucleotide level (> 95% homology). Despite this and the corresponding similarity of amino acid sequence, there are considerable differences in functional and substrate specificity of the two enzymes. In the present study we have examined the role of two amino acids that differ between the two enzymes (147 and 248) to determine the difference between aldosterone synthase and 11 beta-hydroxylase capacity to 11-hydroxylate 11-deoxycorticosterone (DOC). 2. Plasmids containing cDNA encoding wild-type aldosterone synthase, wild-type 11 beta-hydroxylase and mutated forms of aldosterone synthase (D147E and I248T), in which the codons for residues 147 (aspartate exon 3) or 248 (isoleucine exon 4) had been altered to encode the corresponding amino acids (glutamate and threonine respectively) from 11 beta-hydroxylase were transiently expressed in non-steroidogenic COS-7 cells. All transfections were cotransfected with bovine adrenodoxin. Cells were then incubated with [3H]-DOC for 48 h and the production of corticosterone (B), 18-hydroxycorticosterone (18-OHB) and aldosterone measured by measuring tritriated products using thin layer chromatography. 3. Compared with wild-type aldosterone synthase, the mutated form (D147E) encoding amino acid 147 from 11 beta-hydroxylase was more efficient in 11 beta-hydroxylation of deoxycorticosterone (B:DOC ratio 0.53 +/- 0.05 (wild type) to 3.05 +/- 0.37 (mutant); P < 0.001). However, 18-hydroxylation of B and conversion of this steroid into aldosterone were unaffected. There was a 20% increase in the production of aldosterone from DOC (P < 0.05). However, in comparison with wild-type 11 beta-hydroxylase, the mutated aldosterone synthase (D147E) was still less efficient (B:DOC ratio 6.2 +/- 0.41). The mutated aldosterone synthase (I248T) encoding amino acid 248 from 11 beta-hydroxylase showed no changes in conversion of DOC to B or in the production of aldosterone. 4. These data demonstrate that position 147 has an important effect on the efficiency of 11 beta-hydroxylation of DOC and indicate that this is a key difference between the two enzymes in determining functional specificity. However, other residues must also contribute to efficiency of 11-hydroxylation of 11 beta-hydroxylase. In contrast, amino acid 248, which is one of the few differences between the two enzymes in exon 4, does not affect enzyme efficiency. As altered activity of aldosterone synthase and 11 beta-hydroxylase has been proposed as an important intermediate phenotype in essential hypertension, such studies will help our understanding of the structure-function relationships that will be necessary in order to understand how genetic changes may contribute to observed differences in phenotype.

Alteraciones en la enzimología de la producción de aldosterona / Alterations in the enzymology of aldosterone production

El último paso para la producción de aldosterona (11-desoxicorticosterona a aldosterona) en mitocondrias de zona glomerulosa de adrenal de rata es catalizado por la enzima CYP11B2. CYP11B1, en zona fasciculata, transforma 11-desoxicorticosterona en corticosterona o 18-hidroxi-11-desoxicorticosterona. CYO11B1 y CYP11B2 tienen alta homología y sus genes se hallan en tándem en el cromosoma 8q22. Mutaciones en el gen de CYP11B2 y recombinaciones genéticas entre éste y el gen de CYP11B1 serían las responsables de las alteraciones en la enzimología de la producción de aldosterona, dando una nueva denominación y explicación a las deficiencias anteriormente conocidas como de CMOI y CMOII

Alteraciones en la enzimología de la producción de aldosterona / Alterations in the enzymology of aldosterone production

El último paso para la producción de aldosterona (11-desoxicorticosterona a aldosterona) en mitocondrias de zona glomerulosa de adrenal de rata es catalizado por la enzima CYP11B2. CYP11B1, en zona fasciculata, transforma 11-desoxicorticosterona en corticosterona o 18-hidroxi-11-desoxicorticosterona. CYO11B1 y CYP11B2 tienen alta homología y sus genes se hallan en tándem en el cromosoma 8q22. Mutaciones en el gen de CYP11B2 y recombinaciones genéticas entre éste y el gen de CYP11B1 serían las responsables de las alteraciones en la enzimología de la producción de aldosterona, dando una nueva denominación y explicación a las deficiencias anteriormente conocidas como de CMOI y CMOII (AU)

Functional and expression analysis of ovine steroid 11 beta-hydroxylase (cytochrome P450 11 beta).

In this study, the ovine steroid 11 beta-hydroxylase (P450(11 beta) or CYP11B) cDNA previously reported by us (1) was transfected into COS-7 cells. Using 3H-11-deoxycorticosterone (3H-DOC) as the substrate, and paper partition chromatography for separation of steroid products, the expressed enzyme was shown to catalyse the conversion of DOC to corticosterone (B), 18-hydroxy-11-deoxycorticosterone (18-OH-DOC), 18-hydroxy-corticosterone (18-OH-B), and aldosterone (ALDO). These results suggest that the expressed ovine cDNA exhibited 11 beta-hydroxylase, 18-hydroxylase and aldosterone synthesis activities. The enzymatic activity of the enzyme was further analysed by adding unlabelled steroids to compete with 3H-DOC. The conversion of 3H-DOC to 3H-ALDO was inhibited by the addition of excess DOC, B and 18-OH-DOC, indicating that all these steroids were potential substrates of the enzyme. The results also demonstrated that 18-hydroxylation could occur before 11 beta-hydroxylation with this enzyme. However, the addition of excess cold 18-OH-B had no significant effect on the level of 3H-ALDO that was synthesised. This result could imply that 18-OH-B is not an intermediate involved in the conversion of DOC to aldosterone, or, more likely, the enzyme substrate site is not accessible readily. Our results also indicated that DOC was preferred to 18-OH-DOC as a substrate for the enzyme. We have demonstrated by hybridisation histochemistry using specific oligonucleotide probes that the corresponding P450(11 beta) RNA transcript was present in all zones in the sheep adrenal cortex. In summary, we have shown that the enzyme encoded by the predominant P450(11 beta) cDNA isolated from the sheep adrenocortical cDNA library has all the enzymatic activities to biosynthesise ALDO from DOC. The corresponding transcript of this ovine P450(11 beta) cDNA was located throughout the adrenal cortex and thus the inability of the zonae fasciculata-reticularis to secrete ALDO remains to be understood.

Cytochrome P450(11 beta): structure-function relationship of the enzyme and its involvement in blood pressure regulation.

Cytochrome P450(11 beta) is deeply involved in the final steps of biosynthesis of mineralocorticoids. This paper deals with following issues about this enzyme. (1) The structure and function of the enzymes of various animal species are discussed. By making alignment of amino acid sequences of the enzymes, we identified peptide domains essential for the enzyme actions such as a putative steroid binding domain and a heme binding region. Estimates of molecular similarity among the P450(11 beta) family enzymes suggested that the enzymes having both 11 beta-hydroxylation activity and aldosterone (ALDO) synthetic activity of certain animals such as frog, cattle and pig are more similar to the ALDO synthases of the other animals, such as rat, mouse and human, than the 11 beta-hydroxylases of these animals. (2) The molecular nature of the P450(11 beta) family enzymes of genetically hypertensive rats as well as adrenal regeneration hypertension (ARH) rats is examined. (i) Mutation was found in the P450(11 beta) gene of Dahl's salt-resistant normotensive rat. Steroidogenic activity expressed by the mutated gene accounted well for abnormal plasma levels of steroid hormones in this rat. (ii) 11 beta-, 18- and 19-Hydroxylation activities of adrenal mitochondrial prepared from spontaneously hypertensive rat (SHR), Wistar-Kyoto rat (WKY), and stroke-prone (SP)-SHR were not significantly different from each other. Levels of mRNA of ALDO synthase in adrenal glands of 50-week-old SHR was significantly lower than those of 10-week-old SHR, WKY and SHR-SP. (iii) No significant difference in 19-hydroxylation activity was found between adrenal mitochondria prepared from ARH rat and those from control rat. The level of message of ALDO synthase was lower in adrenal glands of ARH rat.

Enzimología de la biosíntesis de aldosterona: una revisión / Enzymology of the biosynthesis of aldosterone: a review

La última etapa de la biosíntesis de aldosterona (ALDO) involucra la oxidación mitocondrial de 11-desoxicorticosterona (DOC), a través de varios caminos, que comienzan en sus metabolicos corticosterona (B) y 18-hidroxi-11-desoxicorticosterona (18OHDOC). Todas las reacciones de estos caminos son catalizadas por enzimas de la familia de los citocromos P450. El número y la identidad de cada una de ellas han sido objeto de investigaciones en los últimos treinta años. El modelo, actualmente en vigencia, postula que en la adrenal de la vaca todas las reacciones que llevan desde DOC a ALDO son catalizadas por un único citocromo P450-11ß/18 hidroxilasa/aldosintetasa, presente en toda la corteza adrenal. En cambio, en la adrenal de rata, ratón y humano, la catálisis total es llevada a cabo por el citocromo P450 CYP11B2 sólo presente en la zona glomerulosa, mientras que en la zona fasciculata existe el citocromo P450 CYP11B1, que sólo cataliza la transformación de DOC en B o en 18 OH-DOC. Este modelo, avalado por experimentos de bioquímica celular y molecular, no explica, sin embargo, algunos hechos experimentales

Enzimología de la biosíntesis de aldosterona: una revisión / Enzymology of the biosynthesis of aldosterone: a review

La última etapa de la biosíntesis de aldosterona (ALDO) involucra la oxidación mitocondrial de 11-desoxicorticosterona (DOC), a través de varios caminos, que comienzan en sus metabolicos corticosterona (B) y 18-hidroxi-11-desoxicorticosterona (18OHDOC). Todas las reacciones de estos caminos son catalizadas por enzimas de la familia de los citocromos P450. El número y la identidad de cada una de ellas han sido objeto de investigaciones en los últimos treinta años. El modelo, actualmente en vigencia, postula que en la adrenal de la vaca todas las reacciones que llevan desde DOC a ALDO son catalizadas por un único citocromo P450-11ß/18 hidroxilasa/aldosintetasa, presente en toda la corteza adrenal. En cambio, en la adrenal de rata, ratón y humano, la catálisis total es llevada a cabo por el citocromo P450 CYP11B2 sólo presente en la zona glomerulosa, mientras que en la zona fasciculata existe el citocromo P450 CYP11B1, que sólo cataliza la transformación de DOC en B o en 18 OH-DOC. Este modelo, avalado por experimentos de bioquímica celular y molecular, no explica, sin embargo, algunos hechos experimentales (AU)