Glycyl-L-proline (gly-pro) is an end product of collagen metabolism that is
further cleaved by prolidase (EC 3.4.13.9); the resulting proline molecule
s are recycled into collagen or other proteins. We postulated a relationshi
p between defective gly-pro hydrolysis, increased collagen degradation and
skin destruction. This relationship was tested using HPLC to measure the gi
g-pro in urine. 24 hour urine samples were collected from 27 old people (86
+/- 6 years old), of whom 15 were suffering from skin pressure sores of th
e sacrum or calcaneus. The urine from patients with pressure sores containe
d significantly more gly-pro than the urine from the control. A cut-off at
7 mu mol/mmol creatinine gave the test a positive predictive value of 70%.
Collagen breakdown was also increased as indicated by the increase of hydro
xyproline (hyp) in the urine. But this breakdown seemed to stop at the gly-
pro step.