Variable pH dependence of the myosin-ATPase in different muscles of the rat.

For the histochemical demosntration of the Myosin-ATPase (EC 3.6.1.3) the pH of both the preincubation and the incubation medium was varied in steps of 1 within a range: 10.2 to 10.5 and 9.3 to 9.9, respectively. The optimum combinations of both pH values, defined as the ones providing most consistent contrast among the three major types of muscle fibers were determined in 9 different muscles of the rat. The spectrum of optimum combinations differs considerably from muscle to muscle. The reduction of the incubation pH by only 0.1 may drastically change the staining pattern. This probably reflects the unspecificity of the histochemical procedure as well as the plasticity of the ATPase systems. To cope with the lability of the myosin-ATPase the optimum pH values of both media should be determined for each muscle separately.