PUTATIVE SYNAPTIC VESICLE NUCLEOTIDE TRANSPORTER IDENTIFIED AS GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE

Synaptic vesicles isolated from electric ray electric organ have been shown previously to contain a 34-kDa protein that binds azido-ATP, azi do-AMP, and N-ethylmaleimide. The protein was found to share similarit ies with the mitochondrial ADP/ATP carrier and assumed to represent th e synaptic vesicle nucleotide transporter. Synaptic vesicles were puri fied by sucrose density gradient centrifugation and subsequent chromat ography on Sephacryl S-1000 from both Torpedo electric organ and bovin e brain cerebral cortex. They contained ATP-binding proteins of 35 kDa and 34 kDa, respectively. ATP binding was inhibited by AMP. Both prot eins were highly enriched after column chromatography of vesicle prote ins on AMP-Sepharose. Antibodies were obtained against both proteins. Antibodies against the bovine brain synaptic vesicle protein of 34 kDa bound specifically to the 35-kDa protein of Torpedo vesicles. An N-te rminal sequence obtained against the 34-kDa protein of bovine brain sy naptic vesicles identified it as glyceraldehyde-3-phosphate dehydrogen ase. The previously observed molecular characteristics of the putative vesicular nucleotide transporter in Torpedo fit those of glyceraldehy de-3-phosphate dehydrogenase. We, therefore, suggest that the protein previously identified as putative nucleotide transporter is, in fact, glyceraldehyde-3-phosphate dehydrogenase.