Activity of dipeptidyl peptidase IV and post-proline cleaving enzyme in sera from osteoporotic patients

The activity of dipeptidyl peptidase IV (EC 3.4.14.5) in human sera from normal controls and osteoporotic patients was assayed with Gly-Pro-4-methylcoumaryl-7-amide (Gly-Pro-MCA) as substrate, at pH 8.7. The mean normal value for the activity in serum of 120 healthy subjects (ages 20-86 y) was 54.0 (SE 0.9, range 34.3-81.6) U/L at 37 degrees C and differed slightly but significantly between the younger group (less than 50 y old) and those older than 50 y. Values for the younger men were slightly but significantly higher than for the older men. Overall, however, the enzyme activities in serum were above normal in patients with osteoporosis. In contrast, the activity of post-proline cleaving enzyme (PPCE) was not increased in serum from patients with osteoporosis, as determined with succinyl-Gly-Pro-4-methylcoumaryl-7-amide (Suc-Gly-Pro-MCA) as substrate. These results suggest that high activities of dipeptidyl peptidase IV in serum of patients with osteoporosis are probably related to its severity.