Butyrate kinase from Clostridium acetobutylicum.

Crude extracts of Clostridium acetobutylicum contain a butyrate kinase of high specific activity (5.2 mumol/min/mg of protein). The enzyme has been purified 77-fold in a six-step procedure to a specific activity of 402 mumol/min/mg of protein. The purified butyrate kinase showed a single band with a molecular weight of 85,000 on nondenaturing polyacrylamide gradient gel electrophoresis. Separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the enzyme is a dimer of two apparently identical subunits with molecular weights of 39,000. The pH optimum for the reaction in the butyryl phosphate-forming direction is 7.5, and the pI of the kinase is 5.6. The amino acid composition of the enzyme is also reported. It contains no tryptophan and is low in sulfur-containing amino acids. The kinase has a broad substrate specificity and exhibits its highest relative activities with butyrate and valerate. Butyrate kinase is rapidly inactivated at 50 degrees C in the absence of a fatty acid substrate. Although a reducing agent was required for maximum activity, treatment with several sulfhydryl-modifying agents failed to inhibit the enzyme.