Regulation of @entity1133 synthesis by acid-base balance in vivo: role of XXXX concentration.

@entity12116 @entity35 @entity1133 @entity3157 @entity520 @entity2865 @entity3104 @entity3655
The purpose of this study was to clarify how changes in acid-base balance influence the rate of @entity1133 synthesis in vivo. Since ureagenesis was increased by an @entity3104 infusion into @entity35 , regulation seemed to be a function of the blood @entity3104 concentration. The rate of @entity1133 synthesis was constant at a fixed rate of @entity3104 infusion and independent of the conjugate base infused, @entity2865 or @entity3157 . The steady-state blood @entity3104 concentration was higher in the @entity35 that developed @entity520 . Thus it appeared that regulation was not directly mediated by this @entity3104 concentration per se. The rate of @entity1133 synthesis was also independent of the blood pH. Accordingly, the rate of @entity1133 synthesis was examined as a function of the plasma @entity3655 concentration. The rate of ureagenesis was found to be directly proportional to the plasma @entity3655 concentration. Assuming that plasma @entity3655 levels reflect those in mitochondria, the @entity3655 concentration yielding half-maximal rates of @entity1133 synthesis (close to 2 microM) was in the same range as Km for the rate-limiting step in ureagenesis, @entity12116 synthetase (EC 6.3.4.16). These results suggest that, at a constant @entity3104 concentration, the decreased rate of ureagenesis caused by a pH fall in vitro could reflect an @entity520 -induced decline in the concentration of true substrate ( @entity3655 ) for this pathway.
