Characterization of alkaline and acid phosphatases from skeletal muscles of young and old rats

Alkaline phosphatase (ALP) and acid phosphatase (ACP) specific activities were measured in gastrocnemius muscles of female Wistar rats ranging in age from 2 to 30 months. ALP activity reached a peak at 12 months, with a subsequent slow decline with age. ACP activity increased sharply up to 12 months of age, followed by a slower elevation up to the age of 30 months. Using histochemical staining techniques and electron microscopy, the presence of ALP was demonstrated in the sarcolemma of gastrocnemius muscles, as well as in some capillaries around muscle fibers. ALP and ACP were isolated further from muscles of young (12 months) and old (30 months) animals by applying ion-exchange chromatography and separation on a Sephadex G-200 column. The purity of ALP was shown on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). From a calibrated Sephadex G-200 column and SDS-PAGE, the molecular mass of ALP was determined as 116 kilodaltons (kDa), a dimer of two 56-kDa monomers. The ACP major peak of the Sephadex G-200 column revealed a molecular mass of 40 kDa. No differences in molecular mass or in amino acid analysis were detected between ALP(s) from young and old animals, indicating that most probably the decline of activity with age is due to some post-translational events, as has been shown in the past for many other enzymes and proteins.