The influence of the nitrogen supply on the structure and activity of glycolate oxidase in Lemna minor L.

Glycolate oxidase, a key photorespiratory enzyme, appears to be influenced by the form of nitrogen supplied to sterile cultures of Lemna minor L. Both its specific activity and molecular weight were doubled in extracts of tissue grown with an ammonium nitrogen source as compared with the enzyme from Lemna grown on nitrate. A study of glycolate oxidase during growth of Lemna on ammonium nitrate revealed a transition from a high-molecular-weight (HMW)- to a low-molecular-weight (LMW)-form apparently correlated with depletion of ammonium ions from the culture-medium and the onset of nitrate uptake. The results are discussed in relation to the possible control of the glycolate pathway.