The Mechanism of The Microbial Hydroxylation of Steroids. Part 1. The C-21 Hydroxylation of Progesterone by Aspergillusniger ATCC 9142

1975 ◽  
Vol 53 (6) ◽  
pp. 845-854 ◽  
Author(s):  
Herbert L. Holland ◽  
Barbara J. Auret
Keyword(s):  
Hydrogen Bond ◽  
Carbonyl Group ◽  
Isotope Effect ◽  
Enol Form ◽  
Deuterium Isotope Effect ◽  
Rate Determining Step ◽  
Microbial Hydroxylation ◽  
Hydroxylation Reaction ◽  
Microbial C

The mechanism of the C-21 hydroxylation of progesterone (1a) by Aspergillusniger ATCC 9142 to give 11-deoxycorticosterone (1b) has been studied by the use of progesterone derivatives and of C-21 deuterium labelled progesterones. The requirement of the C-21 hydroxylase system for a C-20 carbonyl group is demonstrated and the possibility of the involvement of this group, in the C-20,21 enol form, in the C-21 hydroxylation reaction has been discussed. However, on the basis of the observed deuterium isotope effect (KH/KD = 1.25), a mechanism for the microbial C-21 hydroxylation reaction is proposed in which the rate-determining step is the direct insertion of oxygen into a C-21 carbon–hydrogen bond and not one involving enolization of the C-20 carbonyl.In addition, C-11α and C-15β hydroxylation of both 20α- and 20β-hydroxypregn-4-ene-3-one (2a and 2b) by A. niger has been observed.

The mechanism of the microbial hydroxylation of steroids. Part 4. The C-6 β hydroxylation of androst-4-ene-3,17-dione and related compounds by Rhizopusarrhizus ATCC 11145

1978 ◽  
Vol 56 (5) ◽  
pp. 694-702 ◽  
Author(s):  
Herbert L. Holland ◽  
Peter R. P. Diakow
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Enol Form ◽  
Enol Ethers ◽  
Rate Determining Step ◽  
Kinetic Isotope ◽  
Microbial Hydroxylation ◽  
Related Compounds

The steroid analogue 4,4a,5,6,7,8-hexahydro-2(3H)-naphthalenone was hydroxylated at C-8α, C-8β, and C-4a by Rhizopusarrhizus. Similar products were obtained by peracid oxidation of the corresponding enol ethers: hydroxylation of estr-4-ene-3,17-dione by the same fungus occurred at the analogous C-6 and C-10 positions. These results are consistent with a mechanism of microbial hydroxylation involving the enol form of the Δ4-3-ketone. Data from the incubations with R. arrhizus of androst-4-ene-3,17-dione specifically labelled with deuterium at C-4, C-6α, or C-6β and from those of other deuterium labelled substrates have been interpreted in terms of a mechanism of C-β hydroxylation involving a rate-determining step before enolization of the ketone, followed by rapid enolization and oxidation of the enol to give the 6β-hydroxy-Δ4-3-ketone. The kinetic isotope effect, kH/kD, for the hydroxylation of androst-4-ene-3,17-dione at C-6β has been found to be 1.2 ± 0.1.

scholarly journals l-mandelate dehydrogenase from Rhodotorula graminis: comparisons with the l-lactate dehydrogenase (flavocytochrome b2) from Saccharomyces cerevisiae

1993 ◽  
Vol 290 (1) ◽  
pp. 103-107 ◽  
Author(s):  
O Smékal ◽  
M Yasin ◽  
C A Fewson ◽  
G A Reid ◽  
S K Chapman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Lactate Dehydrogenase ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Dimensional Structure ◽  
Striking Difference ◽  
Kinetic Properties ◽  
Proton Abstraction ◽  
Rate Determining Step ◽  
Kinetic Isotope

L-Lactate dehydrogenase (L-LDH) from Saccharomyces cerevisiae and L-mandelate dehydrogenase (L-MDH) from Rhodotorula graminis are both flavocytochromes b2. The kinetic properties of these enzymes have been compared using steady-state kinetic methods. The most striking difference between the two enzymes is found by comparing their substrate specificities. L-LDH and L-MDH have mutually exclusive primary substrates, i.e. the substrate for one enzyme is a potent competitive inhibitor for the other. Molecular-modelling studies on the known three-dimensional structure of S. cerevisiae L-LDH suggest that this enzyme is unable to catalyse the oxidation of L-mandelate because productive binding is impeded by steric interference, particularly between the side chain of Leu-230 and the phenyl ring of mandelate. Another major difference between L-LDH and L-MDH lies in the rate-determining step. For S. cerevisiae L-LDH, the major rate-determining step is proton abstraction at C-2 of lactate, as previously shown by the 2H kinetic-isotope effect. However, in R. graminis L-MDH the kinetic-isotope effect seen with DL-[2-2H]mandelate is only 1.1 +/- 0.1, clearly showing that proton abstraction at C-2 of mandelate is not rate-limiting. The fact that the rate-determining step is different indicates that the transition states in each of these enzymes must also be different.

Partial kinetic ‘resolution’ resulting from a deuterium isotope effect

1991 ◽  
Vol 0 (12) ◽  
pp. 801-802 ◽  
Author(s):  
Panayiotis Anastasis ◽  
Raymond Duffin ◽  
Christopher Gilmore ◽  
Karl Overton
Keyword(s):  
Isotope Effect ◽  
Kinetic Resolution ◽  
Deuterium Isotope Effect
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