|
type |
Journal Article |
authors |
Talwar, R.; Leelavathy, V.; Krishna Rao, J. V.; Appaji Rao, N.; Savithri, H. S. |
title |
Role of pro-297 in the catalytic mechanism of sheep liver serine hydroxymethyltransferase |
journal |
Biochem J |
Activity |
2.1.2.1 |
ui |
20427711 |
year |
(2000) |
volume |
350 Pt 3 |
pages |
849-53. |
| |
keywords |
Animal |
abstract |
Serine hydroxymethyltransferase belongs to the alpha class of pyridoxal- 5'-phosphate enzymes along with aspartate aminotransferase. Recent reports on the three-dimensional structure of human liver cytosolic serine hydroxymethyltransferase had suggested a high degree of similarity between the active-site geometries of the two enzymes. A comparison of the sequences of serine hydroxymethyltransferases revealed the presence of several highly conserved residues, including Pro-297. This residue is equivalent to residue Arg-292 of aspartate aminotransferase, which binds the gamma-carboxy group of aspartate. In an attempt to change the reaction specificity of the hydroxymethyltransferase to that of an aminotransferase and to assign a possible reason for the conserved nature of Pro-297, it was mutated to Arg. The mutation decreased the hydroxymethyltransferase activity significantly (by 85-90%) and abolished the ability to catalyse alternative reactions, without alteration in the oligomeric structure, pyridoxal 5'-phosphate content or substrate binding. However, the concentration of the quinonoid intermediate and the extent of proton exchange was decreased considerably (by approx. 85%) corresponding to the decrease in catalytic activity. Interestingly, mutant Pro-297 Arg was unable to perform the transamination reaction with L-aspartate. All these results suggest that although Pro-297 is indirectly involved in catalysis, it might not have any role in imparting substrate specificity, unlike the similarly positioned Arg-292 in aspartate aminotransferase. |
last changed |
2002/11/04 17:41 |
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