Variations through the day of hepatic and muscular cathepsin A (carboxypeptidase A;EC3.4.12.2), C (dipeptidyl peptidase;EC3.4.14.1) and D (endopeptidase D;EC3.4.23.5) activities and fee amino acids of blood in rats: influence of feeding schedule

Abstract

1. Growing rats were fed either ad lib. or with six (equal) meals offered every 4 h (form 10.00 hours). Rats of each group were killed at intervals of 4 h begining at 11.00 hours. Activities of cathepsin A (carboxy-peptidase A; EC 3.4. 12. 2), C (dipeptidyl peptidase; EC 3.4.14.1) and D (endopeptidase D EC 3.4.23.5) were measured in liver and muscle homogenates and free amino acids in blood were determined.2. In the rats fed ad lib. activities of carboxypeptidase A and endopeptidase D in liber and muscle showed significant variation, with maximum activity in the light period. In general, meal-feeding only caused minor differences in cathepsin activities; although significant differences occurred for carboxypeptidase A. For the latter enzyme a peak in activity occurred in the dark as well as in the light period.3. Irrespective of the feeding schedule, the lower concentration of free essential amino acids of blood occurred generally during the night period. With the controlled-feeding schedule there is an increase of essential amino acids and a slight decrease of non-essential amino acids of blood.