GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE-ACTIVITY AND F-ACTIN ASSOCIATIONS IN SYNAPTOSOMES AND POSTSYNAPTIC DENSITIES OF PORCINE CEREBRAL-CORTEX

1, Glyceraldehyde-3-phosphate dehydrogenase (G3PD) is a glycolytic enz yme that has also been implicated in a wide variety of functions withi n neurons. Because of the well-documented role of G3PD as an actin-bin ding protein, we sought evidence for a G3PD-actin complex in synaptoso mes and postsynaptic densities (PSDs). 2, We have shown G3PD associati on with 0.5-mu m synaptosomal particles by immunofluorescence as simil arly demonstrated for actin (Toh et al., Nature 264:648-650, 1976). An immunoblot analysis also showed G3PD and actin to be enriched in syna ptosomes. Further analysis of subcellular fractions from synaptosomes showed the PSD but not the synaptosomal plasma membranes to be enriche d in G3PD and actin. 3. Highest levels of G3PD catalytic activity were found in synaptosomes and PSDs. Although synaptosomes showed signific ant activity for phosphoglycerate kinase (PGK), an enzyme in sequence with G3PD for ATP production in the glycolytic pathway, no such activi ty was detected in the PSD fraction. 4. Our studies indicate that a G3 PD-actin complex may exist at the synapse, A physical association of G 3PD with endogenous F-actin in synaptosomes and PSDs was demonstrated by combined phalloidin shift velocity sedimentation/immunoblot studies . By this approach, synaptosomal G3PD-actin complexes were also found to be significantly less dense than the PSD G3PD-actin complexes. 5. G 3PD and PGK catalytic activity in synaptosomes suggests a role in glyc olysis, as well as actin binding, in the presynaptic terminals. On the other hand, the high levels of G3PD activity in PSDs but lack of PGK activity suggests that G3PD is involved in nonglycolytic functions, su ch as actin binding and actin filament network organization.