Light-mediated Activation of Nitrate Reductase in Synchronous Chlorella.

The mechanism underlying the sharp increase in activity of nitrate reductase (EC 1.6.6.1) in Chlorella vulgaris forma tertia (strain 211 8k) during the first hour of the 7 hours/5 hours light/dark cycle was investigated. Using the method of density labeling and isopycnic centrifugation, it could be demonstrated that this rapid increase in activity is based on light-mediated activation rather than de novo synthesis of the enzyme. The problematic nature of cycloheximide specificity and models of nitrate reductase activation are discussed.