Demonstration of functional coupling between dopamine synthesis and its packaging into synaptic vesicles.
We have previously shown that the membrane-associated form of the GABA-synthesizing enzyme, glutamate decarboxylase 65 (GAD(65)), is activated by synaptic vesicle proton gradient-mediated protein phosphorylation. We now report that the rate-limiting enzyme in dopamine (DA) biosynthesis, tyrosine hydroxylase (TH), is regulated similarly to GAD(65). The membrane-associated form of TH (MTH) was activated by conditions favoring protein phosphorylation (e.g. ATP) and was inhibited by phosphatase (e.g. calf intestine phosphatase). Furthermore, the ATP-mediated activation of MTH was abolished by conditions that disrupted the proton gradient of synaptic vesicles, e.g. the presence of carbonyl cyanide M-chorophenylhydrazone, gramicidin, or the V-type ATPase inhibitor (bafilomycin), but not the P-type ATPase inhibitor (vanadate). Moreover, DA newly synthesized from tyrosine by MTH and membrane-associated aromatic amino acid decarboxylase was taken up preferentially rather than pre-existing DA. Therefore, the previously proposed model showing close coupling between GABA synthesis and GABA packaging into synaptic vesicles by vesicular GABA transporters is also applicable to the DA system. Hence, it is concluded that there is a general coupling mechanism between neurotransmitter synthesis and packaging of transmitter into synaptic vesicles.
Chen
Rong
R
Department of Pharmacology and Toxicology, University of Kansas, Lawrence, KS, USA.
Wei
Jianning
J
Fowler
Stephen C
SC
Wu
Jang-Yen
JY
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D001921:Brain / Q000378:metabolism*; D002250:Carbon Radioisotopes; D004298:Dopamine / Q000096:biosynthesis*; D005968:Glutamate Decarboxylase / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism*; D008956:Models, Chemical; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism*; D012588:Scintillation Counting; D013552:Swine; D013572:Synaptic Vesicles / Q000378:metabolism*; D014316:Tritium; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors / Q000378:metabolism*
D002250:Carbon Radioisotopes; D007527:Isoenzymes; D014316:Tritium; D000255:Adenosine Triphosphate; D014446:Tyrosine 3-Monooxygenase; D010770:Phosphotransferases; D010744:Phosphoric Monoester Hydrolases; D005968:Glutamate Decarboxylase; C401141:glutamate decarboxylase 2; D004298:Dopamine