HM GCoA reductase was identified in seedlings, callus cultures, cell suspension cultures and in needles of spruce ( Picea abies) (L.) (Karst). Activity was found in both the 18 K pellet and in the 105 K pellet with different ratios between the two fractions from the various sources. The enzyme has a pH-optimum of 7.9 and an absolute requirement for NADPH . The presence of a thiol reagent such as dithiothreitol is required for activity. K m for HM G CoA is 20 -25 μM. Detergents have differential effects on the activity. In seedlings, enzyme activity was considerably higher in the hypocotyls than in the cotyledons. Enzyme activity was high in dark-grown and low in light-grown seedlings. When the light conditions were reversed, levels of activity adapted to the respective new conditions (increase or decline of specific activity). Aerobic incubations of seedlings, callus cultures or needles in medium containing a carbon source, resulted in a large (up to 20-fold) transient increase of HMGCoA reductase activity. Transfer of stationary phase cell suspension cultures into new medium caused a similarly large increase of activity. A number of carbohydrates induced the enzyme, glucose, fructose and sucrose being most effective. The increase of activity was prevented by cycloheximide. All changes of activity were much more pronounced in the 18 K pellet HMG CoA reductase
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Boll et al. (1990) studied this question.