The mineralocorticoid pathway starts with 21-hydroxylation of progesterone to form deoxycorticosterone (DOC). The enzyme in this reaction, 21-hydroxylase, is encoded by the CYP21 gene. 11 , 12 Deoxycorticosterone is then converted to corticosterone through the action of 11β-hydroxylase. There are two distinct 11β-hydroxylase isoenzymes, both of which are encoded by two genes, CYP11B1 and CYP11B2 . 13 Corticosterone is hydroxylated at carbon 18 to form 18-hydroxycorticosterone, which is transformed to aldosterone by removal of two hydrogens (oxidation) at carbon 18. These two reactions are catalyzed by 18-hydroxylase and 18-hydroxysteroid dehydrogenase, respectively, which are encoded by the same gene, CYP11B2 . Transcription of CYP11B1 is regulated primarily by ACTH, whereas angiotensin II regulates CYP11B2 transcription. 14 , 15 Similarly, the glucocorticoid pathway begins with 17α-hydroxyprogesterone, which is converted to deoxycortisol and subsequently to cortisol by 21-hydroxylase and 11β-hydroxylase, respectively, in the same manner as the conversion of progesterone to corticosterone. A deficiency of 21-hydroxylase, 11β-hydroxylase, or 3β-HSD in the adrenals may result in congenital adrenal hyperplasia and female pseudohermaphroditism, manifested as a masculinized female fetus.
The early steps in the biosynthesis of steroids of both plants and animals are the same, except that in plants lanosterol is replaced by the related compound cycloartenol, which contains a three-membered ring (C9, C10, C19) in lieu of the nuclear double bond of lanosterol. The side chains of the phytosterols, such as stigmasterol, and of the sterol ergosterol of yeasts and other fungi contain extra carbon atoms that are incorporated in reactions involving S -adenosylmethionine, which donates methyl groups in numerous biological processes. Although most plant tissues contain only traces of cholesterol, this sterol is the biogenetic precursor of such important plant steroids as the sapogenins , glycosides , and alkaloids . Because pregnane derivatives are intermediates in some of these transformations, plants and animals appear to have important features of steroid metabolism in common.
Steroid isolation , depending on context, is the isolation of chemical matter required for chemical structure elucidation, derivitzation or degradation chemistry, biological testing, and other research needs (generally milligrams to grams, but often more  or the isolation of "analytical quantities" of the substance of interest (where the focus is on identifying and quantifying the substance (for example, in biological tissue or fluid). The amount isolated depends on the analytical method, but is generally less than one microgram.  [ page needed ] The methods of isolation to achieve the two scales of product are distinct, but include extraction , precipitation, adsorption , chromatography , and crystallization . In both cases, the isolated substance is purified to chemical homogeneity; combined separation and analytical methods, such as LC-MS , are chosen to be "orthogonal"—achieving their separations based on distinct modes of interaction between substance and isolating matrix—to detect a single species in the pure sample. Structure determination refers to the methods to determine the chemical structure of an isolated pure steroid, using an evolving array of chemical and physical methods which have included NMR and small-molecule crystallography .  : 10–19 Methods of analysis overlap both of the above areas, emphasizing analytical methods to determining if a steroid is present in a mixture and determining its quantity.