Efficient purification and molecular properties of spinach chloroplast fructose 1,6-bisphosphatase

Improved in vitro light activation and assay systems for two spinach chloroplast enzymes

An improved system for the in vitro light activation of the chloroplast enzymes fructose-1,6-bisphosphatase and NADP-dependent malate dehydrogenase is described. Through the presence of the monothiol beta-mercaptoethanol in the reaction mixtures the activated forms of the enzymes can be stabilized and their activity determined spectrophotometrically.

Studies on the regulatory properties of chloroplast fructose-1,6-bisphosphatase

The regulatory properties of chloroplast fructose-1,6-bisphosphatase (D-fructose-1,6-bisphosphate 1-phosphohydrolase, (EC 3.1.3.11) were examined with a homogeneous enzyme preparation isolated from spinach leaves. The activation of the enzyme, that was earlier shown to occur via reduced thioredoxin, was found to be accompanied by a structural change that took place more slowly than the rate of catalysis. The recently found deactivation of the thioredoxin-activated enzyme by physiological oxidants such as oxidized glutathione and dehydroascorbic acid was also slow relative to catalysis. Under the conditions used, the activated enzyme showed a pH optimum of about 8.0, whereas the corresponding value for the non-activated form was pH 8.8. The importance of the thioredoxin-linked mechanism of enzyme regulation that is effected through photoreduced ferredoxin and ferredoxin-thioredoxin reductase is discussed in relation to other light-controlled regulatory agents in chloroplasts.