ARTICLES

Cytoplasmic dipeptidase activities of kidney, ileum, jejunum, liver, muscle, and blood

Peptide hydrolase activities against glycyl-L-leucine and glycylglycine were investigated in the soluble fractions of blood, liver, kidney cortex, skeletal muscle (gastrocnemius), and jejunal and ileal mucosa of rats. The maximal hydrolase activity in each tissue was determined when the incubation conditions, such as time, pH, substrate and enzyme concentrations, and ionic requirements were optimal. The kinetic constants (apparent Km and Vmax) were determined from Lineweaver-Burk double reciprocal graphs. Maximal hydrolysis rates against both dipeptides were many times greater by kidney and intestinal segments than by those of muscle, liver, or blood. The order of Vmax for hydrolase activity against glycylleucine was kidney greater than ileum greater than jejunum greater than liver greater than muscle greater than blood, and the order against glycylglycine was ileum greater than kidney greater than jejunum greater than liver greater than muscle. Those tissues that had the lowest Vmax values (liver and muscle), when calculated on the basis of tissue weights, were shown to have activities comparable to the others. Results of this study are consistent with our previous findings that: 1) glycylleucine half-life in plasma is shorter than that of glycylglycine, and 2) disappearance rates of these dipeptides from plasma are not affected by nephrectomy or enterectomy.