Rhizopus nigricans, steroid hydroxylation

Rhizopus nigrican (ATCC 6227b) Phycomycetes 1 la-Hydroxylation of steroids, hydroxylation of diteipenes... 

Studies with cell-free hydroxylases suggest that the hydroxylation mechanisms are complex. It is assumed that an electron transport system involving an NADPH-dependent flavoprotein, an iron-sulfur protein, and cytochrome P-450 is involved. In the case of the steroid 15/S-hydroxylase system of Bacillus megaierium, these three components have been demonstrated15. The 1 la-hydroxylase of Rhizopus nigricans is also an enzyme of the P-450 monooxygenase type which works with an NADPH-cytochrome P-450 reductase. In this case the enzyme complex is associated with the endoplasmic reticulum of the mycelial cells34. 

A rational basis for interpreting the regiospecificity of steroid hydroxylation is emerging.12,28,29 With Calonectria decora and Rhizopus nigricans, the orientation of a steroid substrate appears to be controlled by interaction of the oxygen functions with hydrophilic sites (such as A or B) at the active sites of the hydroxylases. Thus, 5 and bind in a similar manner and hydroxylation occurs from the same active site location to give the 11a- or 7a-0H product respectively,28 approximately 5.5 A away from the initial oxygen function. This relationship was also observed in hydroxyla-tions of cyclic alcohols and acylated amines by Sporotrichum sulfures-cens.30... 

Allylic hydroxylation of A -steroids at fee 63-position and A -steroids at the 7-position is possible using a wide range of microorganisms, including Cunninghamella elegans and Rhizopus nigricans. 

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