An investigation into protein digestion with14C-labelled protein

Abstract

Chlorella protein labelled with C14 was fed with glucose to provide 8 [mu]c C14 activity each to rats, or with minced beef heart and peanut oil to provide 200 [mu]c C14 activity each to cats. At intervals from 0-6 hr after feeding samples of portal and sytemic blood were drawn from the rats and 3-4 hr after feeding, similar samples plus mesenteric lymph were drawn from the cats, and C14 activity distribution determined. In rats, maximum activity was attained in the portal blood plasma amino acids between 30 min - 1 hr after feeding, and in the systemic blood 1-2 hr after feeding. Three hours after feeding about 60% of the labelled protein had been assimilated. It was calculated that at least 41% of the C14 absorbed was transported from the intestine as plasma amino acids. Only about 5% of the C14 absorbed could be accounted for as plasma protein. In cats, both protein and amino acid fractions of lymph taken from the mesenteric lymph ducts could account for only a very small proportion of the C14 taken from the intestine.