Rabbit antiserum was prepared against hexokinase isoenzyme type I which was purified from rat brain mitochondria. The antiserum inhibited the activity of the mitochondrial hexokinase type I as well as that of the cytosolic type I enzyme prepared from rat brain, kidney and spleen. It did not, however, inhibit the activity of type II hexokinase from muscle and spleen or that of the type III enzyme from spleen. The results suggest that all hexokinase type I isoenzymes may have a common antigenic site irrespective of their sources, though their responses to a thiol inhibitor are different.
