title: Comparative specificities of Calreticulin Transacetylase to O-acetyl, N-acetyl and S-acetyl derivative of 4-methylcoumarins and their inhibitory effect on AFB1-induced genotoxicity in vitro and in vivo.
abstract: We have earlier conclusively established the Calreticulin Transacetylase (CRTAase) catalyzed modifications of functional proteins such as cytochrome-P450-linked mixed function oxidases (Cyt-P450-linked MFOs), NADPH cytochrome c reductase, and glutathione S-transferase by acetoxy derivatives of polyphenols. In this study, we have investigated the comparative specificities of CRTAase to N-acetyl derivative, 7-acetamido-4-methylcoumarin (7-N-AMC), O-acetyl derivative, 7-acetoxy-4-methylcoumarin (7-AMC), S-acetyl derivative, 7-thioacetyl-4-methycoumarin (7-S-AMC) and their parent compounds in the modulation of catalytic activities of aforesaid proteins. Special attention concentrated on the comparative inhibitory effect of aforesaid acetyl moiety on Cyt-P450-linked MFOs such as 7-ethoxyresorufin O-deethylase (EROD), pentoxyresorufin O-dealkylase (PROD) and aflatoxin B(1) (AFB(1))-induced genotoxicity in vitro and in vivo. The results clearly indicated that N-acetyl and O-acetyl derivatives were better substrates for CRTAase while the S-acetyl was found to be a poorer substrate. Our study involving atomic charge, charge density and molecular electrostatic potential (MEP) calculations indicated the pivotal role of electronegativity and charge distribution values of O, N and S atoms of the acetyl group at C-7 position of the 4-methylcoumarins in CRTAase activity. These facts reinforce our hypothesis that the CRTAase catalyzed modifications of the catalytic activities of aforesaid proteins by acetyl derivative of 4-methylcoumarins is probably due to acetylation of these proteins.
authors.affiliation: Department of Biochemistry, VP Chest Institute, University of Delhi, Delhi 110007, India. ajitvpci@gmail.com
authors.forename: Ajit
authors.initials: A
authors.lastname: Kumar
authors.forename: Prija
authors.initials: P
authors.lastname: Ponnan
authors.forename: Hanumantharao G
authors.initials: HG
authors.lastname: Raj
authors.forename: Virinder S
authors.initials: VS
authors.lastname: Parmar
authors.forename: Luciano
authors.initials: L
authors.lastname: Saso
mesh_terms: D000107:Acetylation; D000123:Acetyltransferases / Q000378:metabolism*; D016604:Aflatoxin B1 / Q000633:toxicity*; D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects; D003374:Coumarins / Q000737:chemistry* / Q000494:pharmacology*; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism; D019362:Cytochrome P-450 CYP2B1 / Q000378:metabolism; D008297:Male; D015162:Micronucleus Tests; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D009152:Mutagenicity Tests; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014468:Umbelliferones / Q000737:chemistry / Q000494:pharmacology
chemical_list: D003374:Coumarins; D014468:Umbelliferones; C032078:4-methylumbelliferyl acetate; D016604:Aflatoxin B1; D019363:Cytochrome P-450 CYP1A1; D019362:Cytochrome P-450 CYP2B1; D009251:NADPH-Ferrihemoprotein Reductase; D000123:Acetyltransferases; C528668:calreticulin transacetylase, rat