Induction and 'superinduction' of sialylation of membrane-bound gamma-glutamyltransferase during liver regeneration.
The present paper shows that in the regenerating rat liver the membrane-bound-gamma-glutamyltransferase exists in two molecular forms. Depending on the state of proliferation, a sialic-acid-rich enzyme (in the fetal or regenerating liver) or a sialic-acid-poor enzyme (in the adult or quiescent liver) could be detected. In regeneration liver (24 h after 2/3 resection) only the sialic-acid-rich or fetal enzyme could be found. Since total enzyme activity (adult + fetal type) remained unchanged, it is assumed that the adult type of gamma-glutamyltransferase was modified by sialylation during the initial phase of liver regeneration. This process of sialylation was prevented by inhibitors of RNA or protein synthesis such as D-galactosamine, actinomycin D or cycloheximide, provided that the inhibitor (D-galactosamine) was given within the first 8 h after partial hepatectomy. Sialylation was not impaired by inhibitors of DNA synthesis, e.g. hydroxyurea or cytosine arabinoside. Administration of actinomycin D during a defined phase of proliferation (24 to 48 h after partial hepatectomy) stimulated the transfer of sialic acid to gamma-glutamyltransferase, a finding which describes for the first time the so-called 'superinduction' of a sialylation process.
D000818:Animals; D004790:Enzyme Induction; D005333:Fetus; D005688:Galactosamine / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008115:Liver Regeneration; D008297:Male; D051381:Rats; D012794:Sialic Acids / Q000378:metabolism*; D005723:gamma-Glutamyltransferase / Q000096:biosynthesis*
D012794:Sialic Acids; D005688:Galactosamine; D005723:gamma-Glutamyltransferase