Histidine degradation enzymes in rat liver: Induction by high protein intake

Abstract

High protein dietary content stimulates urea formation in ureotelic animals but does not exert almost any effect on ammonia production from L-amino acids in vitro. L-histidine and L-threonine are the only amino acids which are most actively deaminated by ureotelic animals fed on a high protein diet. All the steps of L-histidine metabolism have been studied: it has been found that both the histidine transaminase pathway and the histidase pathway are stimulated. Glutamic acid is also a product of histidine catabolism through the histidase pathway, but its catabolism is unaffected by the dietary protein content. These data suggest the existence of independent mechanism controlling the catabolism of the two amino acids.

Plasma amino acid concentrations and mRNA expression of components related to protein degradation in lambs with nutritionally induced metabolic acidosis

“…The increased plasma histidine and plasma arginine concentrations could be a consequence of shifts in glutamate production, as both arginine and histidine can be used as precursors for glutamate formation (Cedrangolo et al 1979;Cynober et al 1995). While elevated arginine may also contribute to the increased plasma urea concentration, examination of amino acids and enzymes that participate in urea cycle function suggest that nutritional induction of metabolic acidosis using NH 4 Cl-treated DDG did not result in any significant changes in overall urea cycle activity.…”