Glyoxylate accumulation

WINGLER, A., LEA, P.J., LEEGOOD, R.C., Photorespiratory metabolism of glyoxylate and formate in glycine-accumulating mutants of barley and Amaranthus edulis, Planta, 1999, 207,518-526. 

Some bacteria, including E. coli, have the full complement of enzymes for the glyoxylate and citric acid cycles in the cytosol and can therefore grow on acetate as their sole source of carbon and energy. The phosphoprotein phosphatase that activates isocitrate dehydrogenase is stimulated by intermediates of the citric acid cycle and glycolysis and by indicators of reduced cellular energy supply (Fig. 16-23). The same metabolites inhibit the protein kinase activity of the bifunctional polypeptide. Thus, the accumulation of intermediates of... 

Oxalate, produced from glycine or obtained from the diet, forms precipitates with calcium. Kidney stones (renal calculi) are often composed of calcium oxalate. A lack of the transaminase that can convert glyoxylate to glycine (see Fig 39.6) leads to the disease primary oxaluria type I (PH 1). This disease has a consequence of renal failure attributable to excessive accumulation of oxalate in the kidney. 

Application of this inhibitor to pea leaves (Miflin et al., 1966) caused glycine, but not glycolate to accumulate. Also, addition of nonradioactive glyoxylate with radioactive glycine stimulated rather than inhibited radioactive serine formation. It was suggested by Miflin et al. (1966), therefore that serine was formed from two molecules of glycine by a mechanism similar to that already known in bacteria and in avian liver [Eq. (4)]. 

The rates of CO2 fixation for both mutants in 1% O2, 0.035% CO2 was similar to those of the wild-type plant. In common with most photorespiratory mutants isolated thus far (2), the rate of both mutants fell to between 30-40% of that of the wild-type on transfer to conditions that promoted photorespiration. The possibility that the decline in the photosynthetic rate is caused by accumulation of amino groups in glycine (17), is strengthened by the run down of glutamate, an amino-donor for transamination of glyoxylate in the peroxisome, detected in both mutants in air. 

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