Interaction of Methyltransferase and Glycine Boronates

Lindquist, Robert

Abstract

The long term objectives of this research are to study the interactions of boronic acid amino acid analogs with appropriate enzyme active sites, and to determine whether such analogs may be enzyme inhibitors of potential physiological significance.
The specific aims of this proposal are as follows. (1) To purify betaine:homocysteine methyltransferase (BHMT) from rat liver and to develop an HPLC assay based upon quantitation of the reactants and products. This enzyme has a central role in methionine biosynthesis and other cellular methylation reactions via S-adenosylmethionine and tetrahydrofolic acid derivatives. (2) To study the inhibition of BHMT by a series boronic acid analogs of N-methylated glycine substrate molecules (II,III). Inhibition, kinetics, pH-Ki profiles and the mono- or biphasic nature of inhibition will be determined as a means of elucidating enzyme active site - inhibitor interactions. (3) To synthesize a series of boronic acid compounds which mimic methylated glycine compounds (I) involved in cellular metabolism. Glycine analogs with boron in place of the methylene carbon (IV) exhibit a multiple of interesting physiological properties including antitumor, hypolipidemic, and antiinflammatory-antiarthritic. Methyl glycine analogs with boron substituted for the carboxyl carbon (II,III) should resemble the substrates for BHMT and are candidates for specific covalent inhibitors as well as potential probes for active site functionalities. Inhibition of BHMT could impair the high rates of transmethylation characteristic of many tumor cells. In addition, analogs II and III may exhibit useful physiological effects in the same manner as compounds of type IV. The boronic acid analog of alanine, (Ala . B), H2NCH(CH3)-B(OH)2, has very recently been reported. It is an effective inhibitor of both alanine- racemase and D-Ala:D-Ala ligase, presumably interacting with one or more groups at the active sites of these enzymes.