Serum phosphohexose isomerase.

In 1933 Lohmann (1) demonstrated the existence of phosphohexose isomerase, the enzyme which mediates the reversible conversion of glucose-6-phosphate to fructose-6-phosphate, in dialyzed frog lnuscle extracts and in simple aqueous extracts of yeast, heart, kidney, liver, and brain. Tank6 (2) and, more recently, Somers and Cosby (3) have found this enzyme to be present in pea meal. Slein (4) has obtained a partially purified preparation of phosphomannose’ isomerase from rabbit muscle. Although several studies have referred to the wide-spread distribution of phosphohexose isomerase in tissues (4, 5), this enzyme has received relatively little investigative attention. The present study shows that a considerable degree of phosphohexose isomerase activity is present in the serum of several species, including man. The properties of this enzyme in human blood serum are characterized, and quantitative data on its activity in various sera from patients with disease are submitted, in order to indicate the possible physiological significance of this enzyme in serum.