Functional Properties of Protein Kinase(s) and Phosphatase(s) Converting Quinate:NAD$Oxidoreductase into Active and Deactivated Forms in Carrot Cell Suspension Cultures

摘要

Quinate:NAD$oxidoreductase (QORase) from carrot cells has been shown to be regulated through reversible phosphorylation. The process involves protein kinase(s) and phosphatase(s) that have the following properties: (1) Protein phosphatase activity is inhibited by NaF but enhanced by Mg2$, even at a relatively low temperature (10°C) and a broad pH range. (2) Protein kinase activity is maximum at pH 8 and is ATP-Mg dependent.The affinity of the enzyme(s) for ATP appears to be high, a two-step process taking place that involves a differential rate of phosphorylation for the various phosphorylatable sites of QORase. From the functional point of view, the reduction of dehydroquinic acid (DHQ) was twice as sensitive to phosphatase(s) as the reverse reaction, the oxidation of quinic acid (QA). The affinity of QORase for DHQ decreased 121-fold when the enzyme was deactivated, whereas its affinity for QA was not modified. The general properties of the QORase-converter enzymes are compared with those of the protein kinases and phosphatases described in the literature