Interaction of Glyceraldehyde Phosphate Dehydrogenase and Aldolase With Microsomal Subfractions of Skeletal-Muscle

We have isolated a protein from the soluble fraction of skeletal muscle which stimulates the formation of triad junctions from isolated transverse tubules and terminal cisternae. This protein has subunit M _r = 34,000 and native M _r = 140,000 and has been identified as glyceraldehyde-3-phosphate dehydrogenase (GAPD). Enzymic activity of GAPD is inhibited when it binds to microsome subfractions. Proteins have been extracted with detergent and salt, from a preparation containing triads and separated by hydroxyapatite chromatography. Calsequestrin shows a specific and potent inhibition of enzyme with a stoichiometry of 0.8 mole calsequestrin/mole tetramer GAPD. The inhibition is relieved in the presence of Ca Cl ₂ . The GAPD competes for the same binding site on microsomal fractions as another extrinsic protein of subunit M _r = 38,000. We have identified the latter protein as aldolase. Aldolase activity is also potentfy inhibited by calsequestrin. Both GAPD and aldolase are predominantly localized in terminal cisternae and T-tubules with a lower but significant content in longitudinal reticulum and "light" terminal cisternae. The ultrastructural distribution of GAPD in isolated organelles and intact muscle has been investigated by electron microscopy using antibodies to the enzyme and protein A labelled with colloidal gold. Supported by NIH training grant HL-07188 , NIH grant AM-21601 and Muscular Dystrophy Fellowship (to RMK).