An interaction between S-Adenosyl-L-methionine and pyridoxal 5′-phosphate, and its effect on Saccharomyces cerevisiae

Abstract

S- Adenosyl- l-methionine (SAM) interacts with pyridoxal 5′-phosphate (PLP) as determined by spectrophotometeric analysis, and this interaction can cause inhibition of PLP-requiring enzymes in vitro. SAM inhibition of tyrosine aminotransferase from Saccharomyces cerevisiae is of a competitive nature with regard to PLP. The apparent K M for PLP is 1.2 · 10 −5 M, and the apparent K 1 for SAM is approximately 1 · 10 −3 M. Evidence of SAM interacting with PLP in vivo was obtained utilizing S. cerevisiae grown in excess methionine. S. cerevisiae overproduces SAM and exhibits growth inhibition when cultured in a medium containing an excess of the amino acid. An analysis of the cofactor and enzyme levels indicates that SAM inhibition of PLP-dependent enzymatic reactions could cause, or contribute to, the growth inhibition.