Mechanism of biochemical action of substituted 4-methylcoumarins. Part 11: Comparison of the specificities of acetoxy derivatives of 4-methylcoumarin and 4-phenylcoumarin to acetoxycoumarins: protein transacetylase.
Our earlier observations led to the identification of a microsomal enzyme termed as acetoxy drug: protein transacetylase (TAase) catalyzing the transfer of acetyl groups from acetylated polyphenols to the receptor proteins. TAase was conveniently assayed by the irreversible inhibition of cytosolic glutathione S-transferase (GST) by the model acetoxycoumarin, 7,8-diacetoxy-4-methylcoumarin (1). The specificities of the acetoxy group on the benzenoid ring and position of the pyran carbonyl group of the coumarin with respect to oxygen heteroatom for the catalytic activity of TAase were also reported earlier. In this communication, we have demonstrated that the acetoxy coumarins and acetoxy dihydrocoumarins having a methyl group instead of a phenyl ring at the C-4, when used as the substrates, resulted in enhancement of TAase activity, while the saturation of double bond at C-3 and C-4 position had no effect on TAase activity. A comparison of the optimized structures of 1 and 7,8-diacetoxy-4-phenylcoumarin (2) suggested that the observed influence may be due to out of plane configuration of the phenyl ring at C-4. Further, the TAase-catalyzed activation of NADPH cytochrome c reductase and inhibition of aflatoxin B1 (AFB1)-DNA binding by acetoxy 4-phenylcoumarins and dihydrocoumarins were significantly lower as compared to those caused by acetoxy 4-methylcoumarins.
Kumar
Ajit
A
Department of Biochemistry, V P Chest Institute, University of Delhi, Delhi 110 007, India.
Singh
Brajendra K
BK
Tyagi
Rahul
R
Jain
Sapan K
SK
Sharma
Sunil K
SK
Prasad
Ashok K
AK
Raj
Hanumantharao G
HG
Rastogi
Ramesh C
RC
Watterson
Arthur C
AC
Parmar
Virinder S
VS
D000107:Acetylation; D000123:Acetyltransferases / Q000378:metabolism* / Q000494:pharmacology*; D016604:Aflatoxin B1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D003374:Coumarins / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D003600:Cytosol / Q000201:enzymology; D004247:DNA / Q000378:metabolism*; D005419:Flavonoids; D005982:Glutathione Transferase / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D010636:Phenols; D059808:Polyphenols; D051381:Rats; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
C114369:7,8-diacetoxy-4-methylcoumarin; D003374:Coumarins; D005419:Flavonoids; D010636:Phenols; D059808:Polyphenols; D004247:DNA; D016604:Aflatoxin B1; C030123:coumarin; D009251:NADPH-Ferrihemoprotein Reductase; D000123:Acetyltransferases; D005982:Glutathione Transferase; D010100:Oxygen