Amino acid sequences of active-site histidine peptides from rabbit muscle phosphoglycerate mutase

Abstract

Monophosphogiyc~rate mutase (MPGM) catalyses the interconversion of 3-phosphoglycerate and 2-phosphoglycerate, in a reaction mechanism involving a pl~osphohistidine illter~nediate [ 1 ,I?]. A correlation of the 2.8 _& resolution electron-density map ffom X-ray crystallographic studies ofyeast MPGM with its amino acid sequence shows 2 histidines at the active site [3]. Structural studies of muscle MGP~I are much less complete, although the enzyme has been used extensively in kinetic work, e.g. [4,5]. The muscle and yeast enzymes have been shown to differ in several respects. The muscle enzyme is a dimer with identical subunits of mol. wt 28 000 [6], whereas the yeast enzyme is isolated as a tetramer composed of 4 identical subunits of mol. wt 27 000 [7]. The activity of the muscle enzyme is sensitive to modification of cysteinyl and arginyl residues [8,9], in contrast to the yeast enzyme that has no thiol [lo], and is only moderately sensitive to butanedione [l l]. In addition, a phosphohistidine peptide isolated from chicken breast muscle MGPM has been sequenced [ 121, and shows no homology with any of the 4 histidine sequences of the yeast enzyme (see table 2). We report here the purification and determination of the amino acid sequences of histidine-containing peptides from rabbit muscle MPGM to obtain an estimate of the extent of structural similarity at the active sites of the muscle and yeast enzymes.