Characterization of a rat liver protein carboxyl methyltransferase involved in the maturation of proteins with the -CXXX C-terminal sequence motif.
We have utilized S-farnesyl-Leu-Ala-Arg-Tyr-Lys-Cys as a methyl-accepting substrate to characterize a membrane-bound C-terminal protein methyltransferase from rat liver. We have localized the activity to the microsomal fraction and show that the bulk of the enzyme fractionates by density gradient centrifugation with glucose-6-phosphatase, a marker of the endoplasmic reticulum, and not with 5'-nucleotidase, a marker of the plasma membrane, or galactosyl:N-acetylglucosamine transferase, a marker of the Golgi apparatus. This methyltransferase appears to form an integral part of the membrane structure. Its activity is markedly affected by a variety of detergents used to solubilize membrane proteins in their native form. All activity is lost when membranes are treated with seven different detergents at a concentration of 1% (w/v). The activity is inhibited by N-ethylmaleimide, although it can be protected against inactivation with its substrate S-adenosyl-L-methionine, or its product S-adenosyl-L-homocysteine. Finally, we find that 5'-methylthioadenosine, a substrate analogue reported to be an inhibitor of this activity in other studies, is not an effective inhibitor in vitro.
Stephenson
R C
RC
Department of Chemistry and Biochemistry, University of California, Los Angeles 90024.
Clarke
S
S
D015720:5'-Nucleotidase / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D003902:Detergents; D003576:Electron Transport Complex IV / Q000378:metabolism; D005260:Female; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D008780:Methyltransferases / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology*; D008930:Mitochondria, Liver / Q000201:enzymology*; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000378:metabolism; D051381:Rats; D013379:Substrate Specificity
D003902:Detergents; D009842:Oligopeptides; C075428:farnesylleucyl-alanyl-arginyl-tyrosyl-lysyl-cysteine; D003576:Electron Transport Complex IV; D008780:Methyltransferases; D015720:5'-Nucleotidase; D005952:Glucose-6-Phosphatase