Coenzyme A Biosynthesis in Plants: Partial Purification and Characterization of Pantothenate Kinase from Spinach

A study of the biosynthesis of coenzyme A (CoA), a critical cofactor in the metabolism of lipids and other molecules in higher plants, was initiated. Pantothenate kinase was partially purified from spinach leaves. This enzyme was predominantly localized in the chloroplast with very little activity observed in the mitochondria or cytosol. DEAE-agarose chromatography resolved two pantothenate kinase activity peaks which differed in their requirement for reductant, stability upon boiling, and reactivity in the presence of spinach holo-acyl carrier protein (ACP) I. One active peak of this enzyme was further purified on Cibacron blue 3GA to yield a preparation containing pantothenate kinase enriched to 20% of the total protein within the fraction. Pantothenate kinase was inhibited by malonyl-CoA, but not by CoASH or acetyl-CoA, and the activity was stabilized by the phosphatase inhibitors sodium molybdate, sodium tungstate, and the phosphatase substrate glycerol 2-phosphate, but was inhibited by sodium fluoride. Further experiments demonstrated a linear increase in pantothenate kinase activity during spinach seed germination, consistent with a role for this enzyme in the developmental utilization of seed triacylglycerol.