COENZYME REPRESSION OF ACETYL-COA CARBOXYLASE BY (+)-BIOTIN

Cell-free sonicated suspensions of L. plantarum were found to have acetyl-CoA carboxylase activity. The product of the reaction, which required ATP, acetyl-CoA and MnCl2 for maximum activity, was identified as malonyl-CoA. Avidin completely inhibited the reaction; the avidin effect was reversed by (+)-biotin. Heated cell extracts had no activity. Citrate and α-glycerophosphate, substances known to activate this enzyme in other organisms, had no effect. Apparent enzyme activity was low in cells grown in levels of (+)-biotin sufficient to support maximum growth. Biotin-deficient and biotin-excess cells showed lower and higher activities respectively. Saturation of biotin-deficient and biotin-sufficient cells with the vitamin, before preparation of extracts, greatly increased activity, whereas no increase was observed after saturation of cells grown with excess biotin. This demonstrated that a major portion of the enzyme in cells grown in sufficient and deficient levels of (+)-biotin is the apoenzyme form; the enzyme of cells grown in excess (+)-biotin is completely in the holoenzyme form. More importantly, the level of apo-acetyl-CoA carboxylase is controlled by the (+)-biotin concentration of the growth medium. Cells grown in excess or sufficient (+)-biotin contained only 20 and 30%, respectively, of the total enzyme (holo-plus apoenzyme) content of deficient cells. Apparently, the coenzyme, (+)-biotin, regulates the level of the protein moiety of the acetyl-CoA carboxylase enzyme. This regulatory mechanism has been termed coenzyme repression.". © 1969."