In bacteria, the enzyme glutamate 5-kinase initiates the biosynthesis of proline by transferring a phosphate group from ATP onto glutamate. The next reaction is catalyzed by the enzyme pyrroline-5-carboxylate synthase (P5CS), which catalyzes the reduction of the ϒ-carboxyl group of L-glutamate 5-phosphate. This results in the formation of glutamate semialdehyde, which spontaneously cyclizes to pyrroline-5-carboxylate. Pyrroline-5-carboxylate is further reduced by the enzyme pyrroline-5-carboxylate reductase (P5CR) to yield a proline amino acid. 
Many of the drugs participating in redox reactions need to be activated before they are effective against their target(s). For example, metronidazole and other nitroimidazoles are broad spectrum drugs that affect a wide variety of anerobic bacteria and protozoa. These drugs are activated by a reduction of the nitro group to an anion radical. The anion radical is highly reactive and will form adjuncts with proteins and DNA leading to a loss of function. In particular, the reactions with DNA result in strand breakage and inhibition of replication and will lead to cell death. Reduction of nitroimidazoles requires strong reducing conditions and anaerobic organisms have more reduction potential than aerobic organisms. This accounts for the selectivity of these compounds for anaerobic organisms. In other words, the drugs are preferentially activated by the pathogens.
Cells of the zona fasciculata and zona reticularis lack aldosterone synthase (CYP11B2) that converts corticosterone to aldosterone, and thus these tissues produce only the weak mineralocorticoid corticosterone. However, both these zones do contain the CYP17A1 missing in zona glomerulosa and thus produce the major glucocorticoid, cortisol. Zona fasciculata and zona reticularis cells also contain CYP17A1, whose 17,20-lyase activity is responsible for producing the androgens, dehydroepiandosterone (DHEA) and androstenedione. Thus, fasciculata and reticularis cells can make corticosteroids and the adrenal androgens, but not aldosterone.