A change in reaction specificity of sheep liver serine hydroxymethyltransferase: induction of NADH oxidation upon mutation of His230 to Tyr

Talwar, Rashmi ; Appaji Rao, N. ; Savithri, H. S. (2000) A change in reaction specificity of sheep liver serine hydroxymethyltransferase: induction of NADH oxidation upon mutation of His230 to Tyr European Journal of Biochemistry, 267 (4). pp. 929-934. ISSN 0014-2956

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Official URL: http://www3.interscience.wiley.com/journal/1191817...

Related URL: http://dx.doi.org/10.1046/j.1432-1327.2000.01085.x

Abstract

Both serine hydroxymethyltransferase and aspartate aminotransferase belong to the α-class of pyridoxal-5′- phosphate (pyridoxalP)-dependent enzymes but exhibit different reaction and substrate specificities. A comparison of the X-ray structure of these two enzymes reveals that their active sites are nearly superimposable. In an attempt to change the reaction specificity of serine hydroxymethyltransferase to a transaminase, His 230 was mutated to Tyr which is the equivalent residue in aspartate aminotransferase. Surprisingly, the H230Y mutant was found to catalyze oxidation of NADH in an enzyme concentration dependent manner instead of utilizing L-aspartate as a substrate. The NADH oxidation could be linked to oxygen consumption or reduction of nitrobluetetrazolium. The reaction was inhibited by radical scavengers like superoxide dismutase and D-mannitol. The Km and kcat values for the reaction of the enzyme with NADH were 74 μm and 5.2 × 10-3 s-1, respectively. This oxidation was not observed with either the wild type serine hydroxymethyltransferase or H230A, H230F or H230N mutants. Thus, mutation of H230 of sheep liver serine hydroxymethyltransferase to Tyr leads to induction of an NADH oxidation activity implying that tyrosyl radicals may be mediating the reaction.

Item Type:Article
Source:Copyright of this article belongs to John Wiley and Sons, Inc.
Keywords:Serine Hydroxymethyltransferase (SHMT); Pyridoxalp; H230; NADH Oxidation
ID Code:21289
Deposited On:20 Nov 2010 13:10
Last Modified:17 May 2016 05:30

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