CYTOCHEMISTRY OF PHOSPHATASES OF THE SARCOPLASMIC RETICULUM

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Abstract
The distribution of the Mg-dependent ATPase associated with a microsomal fraction of rabbit psoas muscle was studied histo-chemically and its localization in relation to the vesicles of the fraction and to the structure of intact fixed muscle was determined. Although enzyme activity was retained after fixation in hydroxyadipal-dehyde and in glyoxal, it was lost after fixation in gluitaraldehyde or after 4 hr. fixation in formaldehyde. Activity was optimally demonstrated when incubations were conducted at 170C, in media containing 125 mM Tris-maleate buffer, pH 7.5, 5 mM ATP, 4 mM MgCl2, and 1 mM Pb(NO3)2. After such incubation, activity was present throughout the sarcoplasmic reticuhim, but was absent from the T-system. Activation by Na or K could not be demonstrated histochemically. However, the otherbiochemical properties of the enzyme in the isolated vesicles and in intact muscle were similar with respect to Mg dependence, substrate specificity, inhibition by Ca, N-ethyl maleimide, p-hydroxymer-curibenzoate, and lack of inhibition by ouabain.