Distribution of sialic acid in frog skeletal muscle and effect of neuraminidase on Ca uptake and ATPase activity of sarcoplasmic reticulum.

The contents of sialic acid in the sarcolemma, sarcoplasmic reticulum (SR) and myofibrils obtained from frog skeletal muscle homogenate were determined. The total sialic acid contents of the sarcolemma and fragmented SR were 2.95 and 3.34 nmols per mg of protein, respectively, while that of myofibrils was 1.47 nmols per mg of protein. Treatment of the fragmented SR with neuraminidase (EC 3.2.1.18; NAase) resulted in the release of sialic acid. Ca uptake and ATPase activity were measured in the NAase-treated fragmented SR. When the fragmented SR stood for 1 hr after treatment and washing, the Ca uptake was decreased slightly and neither basic nor extra ATPase activities were affected. In contrast, when the fragmented SR was allowed to stand for 24 hr after similar treatment, Ca uptake and extra ATPase activity were markedly inhibited, while the duration of extra ATP splitting was markedly prolonged and final ATP hydrolysis was increased without noticeable change in basic ATPase activity. The results obtained suggest that in frog skeletal muscle, sialic acid locates mainly at the surface and SR membranes and that sialic acid is not directly involved in active Ca transport of the SR membrane.