Talwar, Rashmi and Leelavathy, Vijayapandian and Rao, Jala VK and Rao, Naropantul Appaji and Savithri, Handanahal S (2000) Role of pro-297 in the catalytic mechanism of sheep liver serine hydroxymethyltransferase. In: Biochemical Journal, 350 . pp. 849-853.
Serine hydroxymethyltransferase belongs to the a 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 c-carboxy group of aspartate. In an attempt to change the reaction speciÆcity 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 signiÆ-cantly (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 speciÆcity, unlike the similarly positioned Arg-292 in aspartate aminotransferase.
|Item Type:||Journal Article|
|Additional Information:||Mounted on the Internet with permission from Portland Press (2000).|
|Keywords:||proton abstraction;pyridoxal-5´-phosphate;reaction specificity;site-directed mutagenesis|
|Department/Centre:||Division of Biological Sciences > Biochemistry|
|Date Deposited:||06 Sep 2004|
|Last Modified:||19 Sep 2010 04:15|
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