
%0 Journal Article
%A Donadini, Roberta 
%A Copeland, Les 
%T Acetohydroxy acid reductoisomerase of wheat
%J Functional Plant Biology
%D 2000/05/31
%V 27
%N 5
%P 417-423
%K acetohydroxy acid, acetolactate, branched chain amino acid, isomeroreductase, reductoisomerase, Triticum aestivum, wheat.
%R https://doi.org/10.1071/PP99181
%U https://www.publish.csiro.au/paper/PP99181 
%X Acetohydroxy acid reductoisomerase (EC 1.1.1.86, AHAR) was purified to a high degree from green shoots of wheat (Triticum aestivum L. cv. Vulcan). The enzyme was localised in the chloroplasts, and activity was at a maximum approximately 4 d after germination. The subunit molecular mass of wheat AHAR was 57 kD and activity of the native enzyme had an elution volume from size exclusion columns that corresponded to a molecular mass of 47 kD. The enzyme did not require the addition of Mg 2+ ions to reaction mixtures for activity. The Km values for (R,S)-2-acetolactate and (R,S)-2-aceto-2-hydroxybutyrate were 91 and 9 mM, respectively, and the corresponding maximum velocities were 430 and 451 mU mg &#8211;1 protein. The Km for NADPH was approximately 10 mM when either of the acetohydroxy acids was the other substrate. Preparation of the acetohydroxy acid substrates by hydrolysis of the parent esters in strong base led to the formation of inhibitory by-products. Racemisation of the acetohydroxy acids was detected in assay mixtures. 
