Modification of enzyme sulfhydryl groups suppresses UV-induced mutagenesis depending on the nucleotide excision repair system in Escherichia coli B/r WP2

Abstract

S-Methyl methanethiosulfonate (MMTS), which was isolated from cauliflower (Brassica oleracea var. botrytis) homogenate as a potent bio-antimutagen, has been used as an enzyme-sulfhydryl (SH) temporary blocking agent in modification studies of enzyme activities. We examined whether 23 kinds of MMTS-related compounds have a suppressing effect on UV mutagenesis in Escherichia coli B/r WP2. Disulfide derivatives of diphenyl, 2,2′-dipyridine and 4,4′-dipyridine, and N-ethyl maleimide (NEM), which temporarily or tightly block sulfhydryl (SH)-groups, showed similar suppressing effect in E. coli B/r WP2, but not in WP2s hcr−(uvrA−) in the range of nanomolar/plate as MMTS previously did. Cystamine sulfate, methyl methylsulfinylmethyl sulfide and S-methyl-l-cysteinesulfoxide moderately suppressed, and diallyl disulfide and glutathione (oxidized form) weakly suppressed UV mutagenesis in E. coli B/r WP2 in the range of micromolar/plate. MMTS and phorone, a glutathione (GSH)-depleting agent, lowered the intracellular GSH level in E. coli B/r WP2, but phorone did not inhibit UV-induced mutation. These results indicate that the target for SH-modification is enzyme-SHs but not GSH, and that the direct or indirect modification of enzyme-activity by SH-blocking might be involved in the antimutagenesis through a pathway associated with the DNA-excision repair system.