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Light activation of fructose bisphosphatase in photosynthetically competent pea chloroplasts.

ABSTRACT: The fructose bisphosphatase (EC 3.1.3.11) activity of type A chloroplasts isolated from young (9-day-old) pea (Pisum sativum var. Progress no. 9) plants, assayed at physiological pH, substrate and Mg2+ concentrations, increased rapidly on illumination. The enzyme activity detected was more than sufficient to account for observed rates of Co2 fixation both during the induction period and during steady-state CO2 fixation, whether or not dihydroxyacetone phosphate had been added to the preparation. Omission of catalase from the suspension medium had no effect. On switching off the light, CO2 fixation by the chloroplasts ceased at once, yet fructose bisphosphatase activity decreased much more slowly. Changes in enzyme activity were much less marked if assays were conducted at 3 mM substrate and 10 mM-Mg2+. Chloroplasts from older (13--20-day-old) peas only fixed CO2 rapidly if catalase was present in the assay medium. The fructose bisphosphatase activity detected under physiological assay conditions was again more than sufficient to account for observed rates of Co2 fixation. In the presence of added dihydroxyacetone phosphate, however, the rate of Co2 fixation appeared to be determined by the rate of light activation of fructose bisphosphatase. In general, the rates of Co2 fixation and enzyme activation, and the final enzyme activity achieved, decreased markedly with increasing age of the plants. The role of light activation of fructose bisphosphatase as a means of controlling the rate of CO2 fixation in pea chloroplasts is discussed.

SUBMITTER: Charles SA

PROVIDER: S-EPMC1163543 | biostudies-other | 1981 Nov

REPOSITORIES: biostudies-other

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Project description:Clear cell renal cell carcinoma (ccRCC), the most common form of kidney cancer, is characterized by elevated glycogen levels and fat deposition. These consistent metabolic alterations are associated with normoxic stabilization of hypoxia-inducible factors (HIFs) secondary to von Hippel-Lindau (VHL) mutations that occur in over 90% of ccRCC tumours. However, kidney-specific VHL deletion in mice fails to elicit ccRCC-specific metabolic phenotypes and tumour formation, suggesting that additional mechanisms are essential. Recent large-scale sequencing analyses revealed the loss of several chromatin remodelling enzymes in a subset of ccRCC (these included polybromo-1, SET domain containing 2 and BRCA1-associated protein-1, among others), indicating that epigenetic perturbations are probably important contributors to the natural history of this disease. Here we used an integrative approach comprising pan-metabolomic profiling and metabolic gene set analysis and determined that the gluconeogenic enzyme fructose-1,6-bisphosphatase 1 (FBP1) is uniformly depleted in over six hundred ccRCC tumours examined. Notably, the human FBP1 locus resides on chromosome 9q22, the loss of which is associated with poor prognosis for ccRCC patients. Our data further indicate that FBP1 inhibits ccRCC progression through two distinct mechanisms. First, FBP1 antagonizes glycolytic flux in renal tubular epithelial cells, the presumptive ccRCC cell of origin, thereby inhibiting a potential Warburg effect. Second, in pVHL (the protein encoded by the VHL gene)-deficient ccRCC cells, FBP1 restrains cell proliferation, glycolysis and the pentose phosphate pathway in a catalytic-activity-independent manner, by inhibiting nuclear HIF function via direct interaction with the HIF inhibitory domain. This unique dual function of the FBP1 protein explains its ubiquitous loss in ccRCC, distinguishing FBP1 from previously identified tumour suppressors that are not consistently mutated in all tumours.

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Light activation of fructose bisphosphatase in photosynthetically competent pea chloroplasts.

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