Renal Tubular Transport of Proline, Hydroxyproline, and Glycine in Health and in Familial Hyperprolinemia *

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Abstract
Urinary excretion of proline, hydroxyproline and glycine is increased in patients with familial hyperprolinemia, and in normal subjects made sufficiently hyperprolinemic or hyperhydroxyprolinemic. A TMPro. is demonstrable in man; prolinuria is observed when the saturable limit for proline transport is approached. At increased filtered loads, the imino acids also compete for absorptive transport with each other and with glycine, increasing the net excretion of all three substances; other amino acids are not comparably affected. Mutual competition does not necessarily imply a single common transport system for these three substances; multiple transport mechanisms apparently exist, but which must have common functional and structural interrelations.