Ultrastructural Localization of Glycolytic Enzymes on Sarcoplasmic Reticulum Vesicles

TLDR: In this article, electron microscopic immunogold labeling was carried out in isolated sarcoplasmic reticulum (SR) vesicles using specific primary antibodies against selected glycolytic enzymes and Ca 2 1 -ATPase, and appropriate secondary antibodies labeled with 6-nm or 12-nm gold particles.

Abstract: SUMMARY We have previously obtained indirect evidence that sarcoplasmic reticulum (SR) vesicles from cardiac and skeletal muscle contain the complete chain of glycolytic enzymes from aldolase to pyruvate kinase. To investigate directly whether pyruvate kinase and other glycolytic enzymes are anatomically associated with the SR, electron microscopic immunogold labeling studies were carried out in isolated SR vesicles using specific primary antibodies against selected glycolytic enzymes and Ca 2 1 -ATPase, and appropriate secondary antibodies labeled with 6-nm or 12-nm gold particles. Pyruvate kinase was broadly dispersed on the cytoplasmic side of the SR membrane of both cardiac and skeletal muscle vesicles. With 6-nm gold particles, the density of binding to pyruvate kinase was 2522 6 445 and 4171 6 1379 particles/ m m 2 for cardiac and skeletal muscle SR, respectively. Binding densities to Ca 2 1 -ATPase were similar (2550 6 639 particles/ m m 2 for cardiac SR, 3877 6 408 particles/ m m 2 for skeletal muscle SR). Immunogold labeling of ultrathin sections indicated that pyruvate kinase was attached to the SR membrane and located immediately adjacent to the Ca 2 1 -ATPase. Aldolase and glyceraldehyde phosphate dehydrogenase were also found to be attached to the cytoplasmic side of SR vesicles and located in close proximity to Ca 2 1 -ATPase. These results provide the first ultrastructural evidence that glycolytic enzymes are anatomically associated with SR membranes and located near the SR Ca 2 1 -ATPase. The results further support the hypothesis that ATP generated by SR-associated glycolytic enzymes is coupled to SR Ca 2 1 active transport. (J Histochem Cytochem 46:419‐427, 1998)