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4-Aminobut\ rate Aminotransferase.

Authors :
Churchich, Jorge E.
Source :
European Journal of Biochemistry; 9/1/82, Vol. 126 Issue 3, p507-511, 5p
Publication Year :
1982

Abstract

The analogues 5-phospho-pyridoxal-aminooxyacetate and 4-vinyl-pyridoxal 5-phosphate inhibit reduced 4-aminobutyrate aminotransferase reconstituted with pyridoxat 5-phosphate, but they do not affect the catalytic activity of the holoenzyme. The binding of the 5-phosphopyridoxal adducts to the holoenzyme was monitored by measuring the fluorescence properties of the protein and the ligands. The presence of nonequivalent binding sites in reduced samples of enzyme containing 1 mol and 1.8 mol P-pyridoxyl residues/mol dimer was detected by steady and nanosecond fluorescence spectroscopy. The spectroscopic properties (fluorescence lifetime τ = 1 ns, polarization = 0.36 and quantum yield = 0.01) of the first molecule of 5-phosphoapyridoxyl are different from the properties of the second molecule of 5-phospho-pyridoxyl covalently bound to the enzyme (τ = 2.1 ns, P = 0.16, Qτ = 0.1). The spectroscopic properties of pyridoxal 5-phosphate and 5-phospho-pyridoxal-aminooxyacetate bound to different sites on the holoenzyme can be used to deduce proximity relationships between the catalytic sites of 4-aminobutyrate aminotransferase. On the basis of resonance energy transfer measurements, it is proposed that a distance of 27 Å (2.7 nm) separates the two catalytic binding sites. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
00142956
Volume :
126
Issue :
3
Database :
Complementary Index
Journal :
European Journal of Biochemistry
Publication Type :
Academic Journal
Accession number :
15806404
Full Text :
https://doi.org/10.1111/j.1432-1033.1982.tb06809.x