Differential inhibition of rat liver sialyltransferase(s) by various aflatoxins and their metabolites.
Sialyltransferase(s) activity [CMP-N-acetylneuraminic acid:glycoprotein sialyltransferase(s) E.C. 2.4.99.1] was assayed using asialofetuin as a substrate in a total microsomal fraction obtained from rat liver. Rats pretreated with phenobarbital or methylcholanthrene demonstrated a decrease in membrane bound sialyltransferase(s) activity of 27% and 18%,respectively. Microsomes prepared from phenobarbital treated rats were incubated in vitro with aflatoxins B1, B2, B2a, G1, or G2 in the presence or absence of an NADPH generating system. Following this treatment the microsomes were reisolated, washed and assayed for sialyltransferase(s) activity. Aflatoxin B1 and B2a inhibited sialyltransferase(s) by 46% and 55%, respectively, while aflatoxin G1 inhibited sialyltransferase(s) by 54%. Aflatoxins B2 and G2 were only slightly inhibitory. It is proposed that the enzyme inhibition caused by these various aflatoxins is due to binding of these agents to the membranes resulting in a local disruption of the membrane and a change in enzyme conformation.
D000348:Aflatoxins / Q000494:pharmacology*; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D066298:In Vitro Techniques; D008099:Liver / Q000166:cytology / Q000201:enzymology*; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D012799:Sialyltransferases / Q000037:antagonists & inhibitors*; D014166:Transferases / Q000037:antagonists & inhibitors*; D000509:alpha-Fetoproteins / Q000378:metabolism
D000348:Aflatoxins; D000509:alpha-Fetoproteins; D008748:Methylcholanthrene; D014166:Transferases; D012799:Sialyltransferases; D010634:Phenobarbital