PURIFICATION AND CHARACTERIZATION OF SOME METABOLIC EFFECTS OF S-NEPLANOCYLMETHIONINE

  • 1 January 1985
    • journal article
    • research article
    • Vol. 28  (4) , 364-370
Abstract
Our laboratory has previously demonstrated that treatment of mouse L929 cells with 1 .mu.M neplanocin A results in the metabolic formation of S-neplanocylmethionine (Keller, B. T., and R. T. Borchardt, Biochem. Biophys. Res. Commun. 120:131-137 (1984)). The present study describes an efficient procedure for the purification of this analog from L cells based on its inherent chemical stability in alkaline conditions. Several metabolic effects of S-neplanocylmethionine are also reported. In L cells, S-neplanocylmethionine was determined to have an apparent half-life of 13 hr compared to 1 hr for S-adenosylmethionine during the initial 2 hr of a cycloleucine block. Analysis of polyamine levels in neplanocin A-treated cells showed a 3.8-fold decrease in putrescine and a 1.7-fold decrease in spermidine by 24 hr, reflecting a decrease in the cell growth rate in response to neplanocin A rather than a direct effect of S-neplanocylmethionine on the cellular S-adenosylmethionine decarboxylase. Consistent with these results are our findings that S-neplanocylmethionine does not significantly inhibit rat prostate or Escherichia S-adenosylmethionine decarboxylase and that [carboxy-14C] S-neplanocylmethionine exhibits no substrate activity with either enzyme. Purified S-neplanocylmethionine was observed to be a weak inhibitor of both S-adenosylmethionine-dependent protein carboxymethyltransferase and lipid methyltransferase in L cell extracts, having an IC50 value of 205 .mu.M (S-adenosylmethionine = 10 .mu.M). Similar studies with [methyl-3H]S-neplanocylmethionine indicate that the analog has little substrate activity in these two L cell methylation reactions and thus appears to act as a poor competitive inhibitor.