Rat Liver Histidase: Glucose Repression and Half-life after Casein Hydrolysate Feeding

Publisher Website
Google Scholar
Abstract
Histidase, the first enzyme in the major catabolic pathway of histidine, increases in animals fed a large quantity of amino acids but the induction is suppressed if glucose is fed with the amino acids. This investigation was undertaken to determine whether glucose suppression would be influenced by glucagon or cyclic adenosinemonophosphate (c-AMP). Hepatic histidase activity of protein-depleted rats increased twofold within 16 hours after they were force-fed casein hydrolysate, but the increase was prevented if they were force-fed glucose at the same time. Administration of glucagon or dibutyryl cyclic AMP to protein-depleted rats also increased histidase activity, and administration of either of these substances counteracted the glucose repression. The hepatic histidase activity was elevated in alloxan-diabetic rats but decreased significantly when the diabetic animals were treated with insulin. The concentration of liver cyclic AMP increased in rats force-fed casein hydrolysate but not when glucose and casein hydrolysate were fed together. These results suggest that cyclic AMP is involved in the induction of histidase by casein hydrolysate and suppression of this response by force-feeding glucose. The apparent half-life of hepatic histidase in protein-depleted rats force-fed casein hydrolysate was 2.1 days, comparable to the value obtained from measurements on rats fed ad libitum an 80% casein diet for 14 days. Total liver histidase activity was maintained in rats starved for 5 days although total liver protein decreased.