Cyanide Metabolism and {beta}-Cyanoalanine Formation by Washed, Non-proliferating Cultures of Chromobacterium violaceum: Studies with Radiolabeled Cyanide

Department of Biochemistry, University of Liverpool, P.O. Box 147, Liverpool, Merseyside L69 3BX, U.K. ABSTRACT SUMMARY: The fate of radiolabeled cyanide added to washed non-proliferating suspensions of the cyanogenic organism Chromobacterium violaceum was studied. Within 6 h of addition, over 90% of the added cyanide had been metabolized to other compounds, except when L -glutamate alone was included in the suspension medium; in this case only 50% of the added cyanide had been metabolized after 6h incubation. Less than 2% of radioactivity was incorporated into cell material; the rest remained in the suspension medium. The only identified compound into which radioactivity accumulated was β-cyanoalanine. Formation of β-cyanoalanine was stimulated by inclusion of L -glutamate and either O -acetyl- L -serine or L -serine in the incubation medium. Under optimal conditions, approximately 50% of added radiolabel accumulated in β-cyanoalanine. Compounds capable of supplying carbon for growth of C. violaceum were able to substitute, to some extent, for L -glutamate in stimulating β-cyanoalanine synthesis. Both O -acetyl- L -serine and L -serine inhibited β-cyanoalanine formation when included at concentrations in excess of 3 m M . L -Cysteine, L -threonine and L -alanine were unable to substitute for O -acetyl- L -serine or L -serine, and L -cysteine inhibited β-cyanoalanine synthesis. L -Methionine inhibited β-cyanoalanine formation by cells resuspended in cyanide, L -glutamate and O -acetyl- L -serine or L -serine. The effect of growth conditions on the ability of resuspended cells to synthesize β-cyanoalanine was studied. Present address: Tate & Lyle Group R. & D., Philip Lyle Memorial Research Laboratory, P.O. Box 68, University of Reading, Reading, Berks RG6 2BX, U.K.