Compartmentation of glycolytic enzymes in nerve endings as determined by glutaraldehyde fixation

Considerable amounts of five glycolytic enzymes glucosephosphate isomerase, glyceraldehyde-phosphate dehydrogenase, aldolase, pyruvate kinase, and lactate dehydrogenase, became fixed when intact synaptosomes were incubated with glutaraldehyde. Other glycolytic enzymes were immobilized much less by this procedure. The lactate dehydrogenase isoenzymes showed a variable response to glutaraldehyde fixation. The isoenzymes enriched in muscle subunits were rapidly immobilized by glutaraldehyde, while the isoenzymes enriched in heart subunits, especially H4, were not. It is suggested that the enzymes which were immobilized are located near the synaptosomal membrane, perhaps in association with actin, which is found at this site. The enzymes that showed a much smaller degree of fixation were either randomly distributed in the synaptoplasm or less susceptible to fixation.