title: 4-Aminobutyrate aminotransferase fluorescence studies.
abstract: The kinetics of resolution of the pyridoxamine phosphate form of the enzyme 4-aminobutyrate aminotransferase were monitored by fluorescence spectroscopy. 2 mol pyridoxamine phosphate are released/mol enzyme, indicating that two molecules of cofactor are involved in catalysis. The apoprotein is reconstituted by addition of pyridoxal phosphate; the apparent rate constant corresponding to the formation of active species is not a linear function of the concentration of cofactor. A multistep mechanism is proposed for the reconstitution of 4-aminobutyrate aminotransferase. A slow phase of reactivation of the aminotransferase is observed when the apoprotein is allowed to reconstitute in the presence of pyridoxal kinase, ATP and pyridoxal. The enzyme 4-aminobutyrate aminotransferase is a dimeric protein made up of subunits of identical molecular weight. It is characterized by a rotational relaxation time of 110 ns. The dimeric structure does not dissociate into subunits over a wide range of protein concentration (4--0.2 micrometer) at neutral pH.
mesh_terms: D000612:4-Aminobutyrate Transaminase / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000201:enzymology; D007700:Kinetics; D009943:Organophosphorus Compounds; D011732:Pyridoxal Phosphate / Q000494:pharmacology; D011733:Pyridoxamine; D013050:Spectrometry, Fluorescence; D013552:Swine; D000637:Transaminases / Q000378:metabolism
chemical_list: D009943:Organophosphorus Compounds; D011732:Pyridoxal Phosphate; D011733:Pyridoxamine; D000637:Transaminases; D000612:4-Aminobutyrate Transaminase