Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part 4: hyperbolic activation of rat liver microsomal NADPH-cytochrome C reductase by the novel acetylator 7,8-diacetoxy-4-methylcoumarin.
The effect of 7,8-diacetoxy-4-methylcoumarin (DAMC) has been studied on hepatic NADPH cytochrome C reductase-- an enzyme participating in the microsomal electron transport. The preincubation of liver microsomes with DAMC resulted in a time-dependent activation of NADPH cytochrome C reductase. The catalytic activity of the enzyme enhanced nearly 600% by 25 microM concentration of DAMC after 10 min of preincubation. The action of DAMC on the reductase resulted in enhanced v(max) while Km remained constant. A plot of 1/v(max) as a function of DAMC concentration resulted in a non-linear, but rectangular hyperbola indicative of hyperbolic activation. DAMC was also proved to be effective in significantly enhancing the activity of NADPH cytochrome C reductase in vivo. 7,8-Dihydroxy-4-methylcoumarin (DHMC), the deacetylated product of DAMC failed to irreversibly activate the enzyme. The activation effect of DAMC upon the enzyme was abolished by p-hydroxymercury benzoate. The role of a transacetylase in transferring the acetyl group of DAMC to the amino acid(s) of the active site of NADPH cytochrome C reductase causing irreversible enzyme activation is enunciated.
Raj
H G
HG
Department of Biochemistry, VP Chest Institute, University of Delhi, India.
Parmar
V S
VS
Jain
S C
SC
Goel
S
S
Singh
A
A
Tyagi
Y K
YK
Jha
H N
HN
Olsen
C E
CE
Wengel
J
J
D000107:Acetylation; D000818:Animals; D003374:Coumarins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006902:Hydroxymercuribenzoates / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D008956:Models, Chemical; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
C114369:7,8-diacetoxy-4-methylcoumarin; D003374:Coumarins; D006902:Hydroxymercuribenzoates; C030601:4-hydroxymercuribenzoate; D009251:NADPH-Ferrihemoprotein Reductase