Green Tea Catechins: Inhibitors of Glycerol-3-Phosphate Dehydrogenase

Abstract

Green tea catechins, especially (−)-epigallocatechin-3-gallate (EGCG), are known to regulate obesity and fat accumulation. We performed a kinetic analysis in a cell-free system to determine the mode of inhibition of glycerol-3-phosphate dehydrogenase (GPDH; EC 1.1.1.8) by EGCG. GPDH catalyzes the β-nicotinamide adenine dinucleotide (NADH)-dependent reduction of dihydroxyacetone phosphate (DHAP) to yield glycerol-3-phosphate, which serves as one of the major precursors of triacylglycerols. We found that EGCG dose-dependently inhibited GPDH activity at a concentration of approximately 20 μM for 50 % inhibition. The IC₅₀ values of other green tea catechins, such as (−)-epicatechin, (−)-epicatechin-3-gallate, and (−)-epigallocatechin, were all above 100 µM. This suggests a catechin type-dependent effect. Based on double-reciprocal plots of the kinetic data, EGCG was a noncompetitive inhibitor of the GPDH substrates, NADH and DHAP, with respective inhibition constants (Ki) of 18 and 31 µM. Results of this study possibly support previous studies that EGCG mediates fat content.

Key words

green tea - Camellia sinensis - Theaceae - epigallocatechin‐3‐gallate

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1 C.-C. K. and B.-T. W. contributed equally to this work.