Microphotometric measurement of initial maximum reaction rates in quantitative enzyme histochemistry in situ.

Final reaction product formation was recorded microphotometrically for succinate dehydrogenase in cross-sectioned muscle fibers at initial rate conditions and during prolonged incubations. Incubations with gel films and aqueous reaction medium both showed a decline of reaction rates. Maximum reaction rates could only be determined at initial rate conditions during the first minute of the incubation. Reaction rates recorded in different areas of the same tissue section were found to change with time to different degrees. From these results it was concluded that quantitative histochemical measurements of enzyme reactions in situ can only be valid if measured under initial maximum velocity conditions.