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Query: EC:4.1.1.32 (phosphoenolpyruvate carboxykinase)
 4,204 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The interactions of nucleotides with phosphoenolpyruvate carboxykinase were studied by using the stereospecific thiophosphate analogues of GDP and GTP. The metal ion dependent stereoselectivity of these analogues was determined by using steady-state kinetics. The RP and SP isomers of guanosine 5'-O-(1-thiodiphosphate) (GDP alpha S) were substrates with low turnover, and a small preference for the RP isomer was observed. Neither the enzyme-metal nor the nucleotide-metal complex elicited any substantial change in the selectivity. Guanosine 5'-O-(2-thiodiphosphate) (GDP beta S) exhibited no substrate activity for the enzyme, regardless of the cations. This nucleotide was a competitive inhibitor against GDP, however. Both RP and SP diastereomers of guanosine 5'-O-(1-thiotriphosphate) (GTP alpha S) were good substrates for phosphoenolpyruvate carboxykinase; in several cases, depending upon the cation, kcat and/or Vm/Km for the RP isomer is greater than for the substrate GTP. The enzyme-metal complex but not the nucleotide-metal complex affects the relative Km and the Vmax values. In contrast, guanosine 5'-O-(2-thiotriphosphate) (GTP beta S) (SP) is a much better substrate (greater than 50 times) than is GTP beta S (RP). The metal ions have little effect on the selectivity. These results suggest a specific interaction of the beta-phosphate of the nucleotide with the protein. The analogue guanosine 5'-O-(3-thiotriphosphate) (GPT gamma S) serves as a substrate to yield GDP and thiophosphoenolpyruvate. The latter was detected by 31P NMR and was shown to slowly hydrolyze to form phosphoenolpyruvate.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Guanosine thiophosphate derivatives as substrate analogues for phosphoenolpyruvate carboxykinase. 391 4

Renal adaptation to chronic metabolic acidosis was studies in Arbor Acre hens receiving ammonium chloride by stomach tube 0.75 g/kg/day during 6 days. During a 14-day study, it was shown that the animals could excrete as much as 60% of the acid load during ammonium chloride administration. At the same time urate excretion fell markedly but the renal contribution to urate excretion (14%) did not change. During acidosis, blood glutamine increased twofold and the tissue concentration of glutamine rose in both liver and kidney. Infusion of L-glutamine led to increased ammonia excretion and more so in acidotic animals. Glutaminase I, glutamate dehydrogenase, alanine aminotransferase (GPT), and malic enzyme activities increased in the kidney during acidosis but phosphoenolpyruvate carboxykinase (PEPCK) activity did not change. Glutaminase I was not found in the liver, but hepatic glutamine synthetase rose markedly during acidosis. Glutamine synthetase was not found in the kidney. Renal tubules incubated with glutamine and alanine were ammoniagenic and gluconeogenic to the same degree as rat tubules with the same increments in acidosis. Lactate was gluconeogenic without increment during acidosis. The present study indicates that the avian kidney adapts to chronic metabolic acidosis with similarities and differences when compared to dog and rat. Glutamine originating from the liver appears to be the major ammoniagenic substrate. Our data also support the hypothesis that hepatic urate synthesis is decreased during acidosis.
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PMID:The kidney of chicken adapts to chronic metabolic acidosis: in vivo and in vitro studies. 681 56