Ubiquitin-mediated degradation of tyrosine aminotransferase (TAT) in vitro and in vivo.
Degradation of a protein via the ubiquitin proteolytic pathway involves two successive steps. Covalent attachment of ubiquitin to the target protein and degradation of the tagged substrate by the 26S proteasome. Most native cellular proteins that are targeted by the ubiquitin system are short-lived transcriptional activators and growth and cell cycle regulators, as well as unstable membrane proteins. In the present study we demonstrate the involvement of the system in the degradation of tyrosine aminotransferase (TAT), a key enzyme in intermediary metabolism. In vitro, we have shown that the native enzyme is conjugated and degraded in a system that requires ATP and ubiquitin. Degradation was monitored by following the decrease of catalytic activity as well as disappearance of the protein molecule. The enzyme could be protected from degradation by association with its specific cofactor, pyridoxal phosphate (PLP). In vivo, we prepared cell extracts from livers of animals in which TAT was induced by starvation and corticosteroid administration. The dramatic increase in the level of the enzyme was accompanied by a concomitant increase in the level of specific TAT-ubiquitin adducts.
Ciechanover
A
A
Department of Biochemistry and the Rappaport Institute for Research in the Medical Sciences, The Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa.
Hargrove
J L
JL
Gross-Mesilaty
S
S
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002457:Cell Extracts; D008099:Liver / Q000201:enzymology; D008956:Models, Chemical; D010447:Peptide Hydrolases / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D011732:Pyridoxal Phosphate / Q000378:metabolism; D051381:Rats; D014444:Tyrosine Transaminase / Q000378:metabolism*; D014452:Ubiquitins / Q000378:metabolism*
D002457:Cell Extracts; D014452:Ubiquitins; D011732:Pyridoxal Phosphate; D000255:Adenosine Triphosphate; D014444:Tyrosine Transaminase; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease