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PubMed1989

Regulation of gene expression by insulin in adipose cells: opposite effects on adipsin and glycerophosphate dehydrogenase genes.

Insulin is known to play the role of a positive effector both in vitro on the adipose conversion process and in vivo on the fatty acid synthesis and esterification processes in adipose tissue. The effects of insulin on the expression of two genes activated during adipose conversion, glycerol-3-phosphate dehydrogenase (GPDH) and adipsin genes, have been investigated in 3T3 F442A adipose cells. Within a physiological range of concentrations, insulin exerts opposite effects on the levels of GPDH (EC50 approximately 0.2 nM) and adipsin (EC50 approximately 1 nM) mRNAs. Its negative effect on the abundance of adipsin mRNA involves primarily a rapid inhibition of the transcriptional rate (less than 2 h). Its positive effect on the abundance of GPDH mRNA is due to a stimulation of the transcriptional rate accompanied by a delayed stabilization of GPDH mRNA. In addition, insulin exerts a specific effect on the length of the poly(A) tract of the adipsin mRNA. These results show that a single mechanism for the regulation of adipose-related genes by insulin can be excluded but rather suggest a complex phenomenon in which various levels of regulation take place.

Adipose Tissue↗
PubMed2002

Dependency of sugar transport and phosphorylation by the phosphoenolpyruvate-dependent phosphotransferase system on membranous phosphatidyl glycerol in Escherichia coli: studies with a pgsA mutant lacking phosphatidyl glycerophosphate synthase.

It has been reported that phosphatidyl glycerol (PG) is specifically required for the in vitro activities of the hexose-phosphorylating Enzymes II of the Escherichia coli phosphoenolpyruvate-dependent sugar transporting phosphotransferase system (PTS). We have examined this possibility by measuring the properties of a null pgsA mutant that lacks detectable PG. The mutant showed lower in vitro phosphorylation activities towards several sugars when both PEP-dependent and sugar-phosphate-dependent [14C]sugar phosphorylation reactions were measured. The order of dependency on PG for the different enzymes II was: IIMannose > IIGlucose > IIFructose > IIMannitol. Nonsedimentable (40000 rpm for 2 h) Enzymes II exhibited a greater dependency on PG than pelletable Enzymes II. Western blot analyses showed that the glucose Enzyme II is present in normal amounts. Transport and fermentation measurements revealed diminished activities for all Enzymes II. Thermal stability of all of these enzymes except the mannitol-specific Enzyme II was significantly decreased by the pgsA mutation, and sensitivity to detergent treatments was enhanced. Sugar transport proved to be the most sensitive indicator of proper Enzyme II-phospholipid association. Our results show that PG stimulates but is not required for Enzyme II function in E. coli.

Biological Transport↗
PubMed1993

Metabolite-modulated complex formation between alpha-glycerophosphate dehydrogenase and lactate dehydrogenase.

A modified Hummel-Dreyer equilibrium chromatography technique was used to test the hypothesis that NADH induces the molecular association of lactate dehydrogenase (LDH) and alpha-glycerol-3-phosphate dehydrogenase (alpha-GDH). In the presence of a very limited NADH concentration, a unique elution profile with a new peak running immediately ahead of a trough at the free alpha-GDH elution position is obtained. The appearance of this peak-trough profile is physical evidence that reversible association between LDH and alpha-GDH occurs over a very limited range of free NADH concentrations. The association constant for this complex formation between LDH and alpha-GDH is estimated to be 2.0 microM-1. With the NADH concentration increased to saturation level, no evidence of binding is observed. Such concentration-dependent behavior suggests that the strong competition between LDH and alpha-GDH for the limited amount of NADH tends to promote the enzyme-enzyme contact in order to make the most efficient use of the shared metabolite. The experimental results described in this article make a convincing argument for a metabolite-modulated enzyme-enzyme interaction along this metabolic pathway.

Binding, Competitive↗