Inhibition of Plant Lactate Dehydrogenase Isoenzymes by Benzoic Acid and Cinnamic Acid Derivatives

Abstract

Several phenolic compounds such as derivatives of benzoic and cinnamic acid were investigated with respect to their inhibitory effect on potato tuber lactate dehydrogenase isoenzymes. Ki values were determined and it was found that they were in the range of 10−2 M for several benzoic acid derivatives while they were in the range of 10−5 M for several hydroxylated cinnamic acid derivatives such as 3,4-dihydroxy cinnamic acid, p(m)nitrocinnamic acid, and 7,8-dihydroxy-4-methyl coumarin as well as kynurenic acid. Also coumaric acid derivatives revealed a very strong inhibition: The K1 values for coumarin and p-coumaric acid were in the range of 10−4 M. The inhibition by all aromatic compounds tested was found to be of the non competitive type. In contrast to mammalian LDH, potato tuber LDH isoenzymes were not inhibited seriously by oxamate and oxalate. Also several amino acids as well as acids from the tricarboxylic acid cycle did not influence the activity of plant LDH isoenzymes.