Gluconeogenesis from lactate was studied in perfused livers from phenobarbital-pretreated rats fasted for 24 h. Maximal rates of glucose production obtained with lactate concentrations of more than 2 mM were suppressed to about 50°/, following the addition of aminopyrine, a substrate for NADPH-utilizing mixed-function oxidations. Submaximal rates (i.e. with 0.5-2 mM lactate) or gluconeogenesis from dihydroxyacetone were only slightly affected by aminopyrine, whereas no inhibition was observed a t low gluconeogenic rates. The data are consistent with the following hypothesis. I n the presence of active NADPH-utilizing processes (such as mixed-function oxidation of aminopyrine) a futile cycle involving malic enzyme occurs in the pathway of gluconeogenesis which is compensated for by an increased flux through the pyruvate carboxylase reaction. Thus, gluconeogenesis is suppressed when maximal activity of pyruvate carboxylase is reached. It is assumed that the observed inhibition of gluconeogenesis is not specific for mixed-function oxidation, but mav be an example for a more general mechanism of metabolic interdependences involving the extramitochondria1 NADPH p&l.
An easy to perform, rapid and precise assay for invertase is introduced. In it enzyme activity is determined spectrophotometrically from a coupled enzymatic reaction.
Ein kontinuierlicher spektrophotometrischer Test für die DünndarminvertaseZusammenfassung: Ein einfacher, rasch durchfuhrbarer und präziser Test für Invertase wird vorgestellt. In ihm wird die Enzymaktivität spektrophotometrisch anhand einer gekoppelten enzymatischen Reaktion gemessen.
Endogenous and postheparin monoglyceride hydrolase (MGH) was studied in 9 patients with acute virus hepatitis and in 25 normal subjects with the use of a new spectrophotometric method. During the 4 weeks of observation the patients had significantly higher endogenous and reduced postheparin MGH levels if compared with the controls (p smaller than 0.001). In the initial phase of hepatitis the alterations were more pronounced and the serum glyceride concentration was raised. The results show that MGM activities in plasma may be greatly influenced by the liver.
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