Further studies on a unique T-tubular acid phosphatase in avian skeletal muscle

With the unique observation, using conventional cytochemistry, of acid phosphatase reaction production in the T-tubules of the posterior latissimus dorsi muscle of the chicken, the possibility of endocytosis of lysosomal enzymes by muscle cells came into question. After testing the substrate specificity of this T-tubular phosphatase, it was clear that the enzyme hydrolysed glucose 6-phosphate and beta-glycerophosphate at pH 5.0 but not cytidine-5'-monophosphate which was hydrolysed by dense bodies and autophagic vacuoles. The cytochemical evidence points to a unique phosphatase present on muscle cell membranes which apparently does not belong to the vacuolar apparatus of skeletal muscle and is not 5'-nucleotidase.