Partial acid hydro lysates of proteins; assay of liquid protein hydro lysates in protein-depleted rats.

Experiments to determine the comparative nutritive value of partial acid hydrolysates of various proteins have been carried out for several years in this laboratory. Most of this work has involved studies of nitrogen balance in dogs wherein the hydrolysates were administered intravenously. Short term experiments, i.e. 4 to 5 days, were used to determine minimum nitrogen levels at wb.ich the N balance could be maintained (1,2). In these experiments 2, 4, and G hour hydrolysates of casein and fibrin (3) all appeared to be well utilized and capable of maintaining the balance at levels of 120 to 150 mg. of N per kilo per day. The casein hydrolysates did not support the balance at this low level unless fortified with sulfur amino acids. In subsequent longer term experiments (4) fibrin hydrolysates proved adequate to support dogs in nitrogen balance at a level of 120 mg. of N per kilo per day for 15 weeks, whereas dogs on somewhat higher levels of casein hydrolysate failed completely in a few weeks. On the basis of these and other experiments it was concluded that short term nitrogen balance studies in normal adult dogs may be misleading and that long term experiments at low levels of nitrogen are more significant. Another method of approach tested the ability of hydrolysates to bring about rapid recovery of severely depleted dogs when given in massive dosage (5). In these studies partial acid hydrolysates of fibrin were again better utilized than those of casein. Because the casein and fibrin hydrolysates did not appear to differ markedly in essential amino acid value (5), it was deduced that the better utilization of fibrin hydrolysate might be due to better utilization of the bound (peptide) amino acids of fibrin hydrolysate. Christensen, Lynch, Decker, and Powers (6) have reported a somewhat lower excretion of bound amino acids in humans following infusion of partial acid hydrolysates of fibrin than after infusion of an enzymatic digest of casein. These findings point to the need for intravenous studies in the final assessment of intravenous hydrolysates which contain a significant proportion of their total amino acids in bound form.