抄録
Acetate kinase (AK) of Bacillus stearothermophilus is a tetrameric enzyme composed of 4 identical subunits each having a molecular weight of 40, 000. It gave sigmoidal kinetics with respect to ATP. The native enzyme was hybridized with the succinylated enzyme in order to clarify the subunit structure as well as the relationship between the structure and function of this enzyme. The succinylation of the enzyme was performed with succinic anhydride. Succinylated AK thus obtained had no enzymatic activity. When a mixture of the native and succinylated enzymes was treated with 6m guanidine hydrochloride and dialyzed, only one species of hybrid was obtained. The specific activity and extent of succinylation of the hybrid enzyme were intermediate between those of reconstituted and succinylated enzymes. These results show that hybrid AK is composed of two native and two succinylated subunits.
Hybrid AK had sigmoidal kinetics quite similar to those of reconstituted AK. This suggests that the combination of two subunits is necessary for allosteric behavior. These observations, taken together with the data that 4 mol of alanine was found as the N-terminal amino acid, suggest that acetate kinase of B. stearothermophilus is an (A)2-(A)2 type tetramer consisting of identical subunits.
This conclusion was supported by the results of crosslinking of this enzyme using a bifunctional reagent, hexamethylene diisocyanate.
