The phosphoglycerate mutase family is generally very well documented with respect to structure, evolution, and mode of action. However, a few individuals in the family remain relatively poorly characterized and will clearly require more detailed study. Furthermore, certain aspects of the detailed behavior of these enzymes are, as yet, incompletely understood and require further investigation. Cofactor-dependent monophosphoglycerate mutase and bisphosphoglycerate mutase are undoubtedly very closely related. Their amino acid sequences are strongly similar, they can form active heterodimers, and they catalyze the same three reactions, albeit at substantially different relative rates. Both enzymes catalyze a ping-pong type of reaction with a phosphohistidine intermediate. The presence of an additional phospho ligand at the active site of monophosphoglycerate mutase helps to explain why this enzyme is better at retaining the 2,3-bisphosphoglycerate intermediate and why it is thus more efficient (by a factor of about 10(3)) at catalyzing the interconversion of 3- and 2-phosphoglycerates. The reason why 1,3-bisphosphoglycerate is a better substrate for bisphosphoglycerate mutase than for monophosphoglycerate mutase (by a factor of about 30) is not yet apparent but presumably relates to the relative positioning of the two phospho-binding sites. Both enzymes are equally good as phosphatases when the reaction is activated by 2-phosphoglycollate. Available evidence indicates that these mutases are similar in many respects to the much smaller, cofactor-dependent monophosphoglycerate mutase from Schizosaccharomyces pombe, but further information is required to define the relationship more precisely. Cofactor-independent monophosphoglycerate mutase belongs to a quite distinct branch of the phosphoglycerate mutase family. It is not known at present whether this branch is related divergently or convergently to the cofactor-dependent monophosphoglycerate mutase/bisphosphoglycerate mutase branch. Existing evidence can be argued both ways. For example, the kinetic evidence shows a ping-pong type of reaction and would be consistent with a phosphohistidine intermediate as encountered in the other mutases. Thus the cofactor-independent enzyme may also have arisen by gene duplication--but, in this case, yielding an enzyme of about twice the size, with slightly different residues at the active site and C-terminal tail. An alternative possibility, of course, is that the two branches of the phosphoglycerate mutase family are quite unrelated in a divergent sense and are little more similar structurally than is, for example, the catalytically similar enzyme phosphoglucomutase.(ABSTRACT TRUNCATED AT 400 WORDS)