Differential kinetic properties of L-2-amino-4-methylthio-cis-but-3-enoic acid, a methionine analog inhibitor of S-adenosylmethionine synthetase.
The L-methionine analog, L-2-amino-4-methylthio-cis-but-3-enoic acid (L-cisAMTB), was examined as a potential inhibitor of the enzyme, S-adenosylmethionine (AdoMet) synthetase. The rational design of L-cisAMTB was based on previously observed potent enzyme inhibitory activity for its closely related structural analog, L-2-amino-4-methoxy-cis-but-3-enoic acid (L-cisAMB). The kinetic behavior of L-cisAMTB was studied using AdoMet synthetase isozymes I and II fractionated from L1210 murine leukemia cells. L-cisAMTB, which was a competitive inhibitor with respect to L-methionine, gave apparent Ki values of 21 and 5.7 microM for isozymes I and II, respectively. These values indicate that L-cisAMTB was slightly less inhibitory than L-cisAMB. L-cisAMTB was also a substrate for the AdoMet synthetase reaction, with respective Km values of 555 and 33 microM for isozymes I and II. In the absence of added inhibitors, the activity of isozyme II, but not isozyme I, was stimulated 2.5-fold by the presence of 10% DMSO. This preferential stimulation of isozyme II and the highly significant difference in Km values of L-cisAMTB for isozymes I and II point to possible physical differences in these tumor isozymes that were not apparent in earlier studies.
Grace Cancer Drug Center, Roswell Park Cancer Institute, Buffalo, NY 14263.
J R
JR
Sufrin
J B
JB
Lombardini
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Alks
D000818:Animals; D002460:Cell Line; D004121:Dimethyl Sulfoxide; D007527:Isoenzymes / Q000037:antagonists & inhibitors* / Q000378:metabolism; D007700:Kinetics; D007939:Leukemia L1210 / Q000201:enzymology; D008715:Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology; D008716:Methionine Adenosyltransferase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051379:Mice
D007527:Isoenzymes; C083253:2-amino-4-methylthio-3-butenoic acid; D008715:Methionine; D008716:Methionine Adenosyltransferase; D004121:Dimethyl Sulfoxide