The effect of lead on the calcium-handling capacity of rat heart mitochondria.

1. Glucose 6-phosphate dehydrogenase (D-glucose 6-phosphate-NADP+ oxidoreductase, EC 1.1.1.49) from baker's yeast (Saccharomyces cerevisiae) was immobilized on CNBr-activated Sepharose 4B with retention of about 3% of enzyme activity. This uncharged preparation was stable for up to 4 months when stored in borate buffer, pH7.6, at 4 degrees C. 2. Stable enzyme preparations with negative or positive overall charge were made by adding valine or ethylenediamine to the CNBr-activated Sepharose 4B 30min after addition of the enzyme. 3. These three immobilized enzyme preparations retained 40-60% of their activity after 15 min at 50 degrees C. The soluble enzyme is inactivated by these conditions. 4. The soluble enzyme lost 45 and 100% of its activity on incubation for 3h at pH6 and 10 respectively. The three immobilized-enzyme preparations were completely stable over this entire pH range. 5. The pH optimum of the positively and negatively charged immobilized-enzyme preparations were about 8 and 9 respectively. The soluble enzyme and the uncharged immobilized enzyme had an optimum pH at about 8.5 6. Glucose 6-phosphate dehydrogenase immobilized on CNBr-activated Sephadex G-25 was unstable, as was enzyme attached to CNBr-activated Sepharose 4B to which glycine, asparitic acid, valine or ethylenediamine was added at the same time as the enzyme.