3-Hydroxy-3-methylglutaryl coenzyme A reductase (NADPH) was solubilized by trypsin digestion from sliced potato tuber microsomes, and purified to apparent homogeneity in the absence of detergent with a recovery of 1.8%. The enzyme had a specific activity of 7,910 nmol of mevalonate formed per min per mg of protein. On molecular-sieving high-performance liquid chromatography, the activity was coincident with the single protein peak corresponding to a molecular weight of approximately 110 kDa. On SDS-polyacrylamide gel electrophoresis, the purified enzyme showed only one protein staining band corresponding to a molecular weight of approximately 55 kDa. The apparent Km value for S-HMG-CoA was 6.4 microM and that for NADPH was 25 microM.

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