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J. Biol. Chem., Vol. 266, Issue 31, 20761-20766, Nov, 1991

Arrangement of the substrates at the active site of brain pyridoxal kinase

WF Wolkers, JD Gregory, JE Churchich and EH Serpersu
Department of Biochemistry, University of Tennessee, Knoxville 37996- 0840.

The distances between enzyme-bound paramagnetic CrATP (a stable, beta, gamma-bidentate complex of Cr3+ and ATP) at the active site of sheep brain pyridoxal kinase and the protons of bound inhibitor 4-dPyr (4- deoxypyridoxine) were determined in the ternary enzyme-CrATP.4-dPyr complex by measuring the paramagnetic effects of Cr3+ on the longitudinal relaxation rates (1/T1p) of the protons of 4-dPyr. The correlation time for the Cr(3+)-4-dPyr dipolar interaction on the enzyme was estimated as 1.59 ns by the frequency dependence of 1/T1p of water protons. Temperature dependence of 1/T1p values indicated the fast exchange of 4-dPyr from the paramagnetic enzyme.CrATP.4-dPyr complex; hence the measured 1/T1p values can be used for metalnucleus distance determinations. The distances from the Cr3+ of the enzyme- bound CrATP to the 2-methyl (7.19 A), 4-methyl (7.18 A), and H6 proton (6.18 A) of the 4-dPyr are too great to permit a direct coordination of any group from 4-dPyr. However, these distances can be built into a model in which phosphorus of the gamma-phosphoryl group of ATP is 4 A away from the oxygen atom of the 5-CH2OH group of the 4-dPyr. This suggests that phosphorylation of pyridoxal can occur via direct transfer of the phosphoryl group between the bound substrates at the active site of pyridoxal kinase.
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