1994 Volume 58 Issue 5 Pages 822-825
A DNA polymerase has been assayed from chloroplasts of petunia plants cultured in vitro. The enzyme activity depends on the presence of DNA and Mg2+ and is stimulated by K+. A single DNA polymerase band of 75 kDa was shown by SDS-polyacrylamide gel electrophoresis using a DNA-containing gel followed by in situ renaturation of proteins and incubation of the intact gel in a polymerase assay mixture. The enzyme activity was inhibited by N-ethylmaleimide (59% at 1mM) and dideoxythymidine triphosphate (25% at a ratio ddTTP/dTTP 1 : 1). The inhibitory effects of flavonoids on the DNA polymerase activity were studied. The glycosylation of hydroxyl groups on the flavonoids resulted in compounds that behaved as gradually weaker inhibitors with increased size of the substituent. The degree of inhibition decreased in the following order : quercetin > quercetin-3-L-rhamnoside > quercetin-3-rutinoside. Similarly baicalein-7-D-glucuronide was less active than baicalein. On the other hand, the number and position of hydroxyls of A ring was important for the inhibitory capacity. The flavonoids with a greater number of hydroxyl groups were more potent inhibitors of the chloroplast DNA polymerase.
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