Studies on D-Tetrose Metabolism

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Abstract
A procedure for the purification of D-erythrulose reductase from beef liver is described. D-Erythrulose reductase was purified approximately 1,700-fold from acetone powder extracts of beef liver. The purified enzyme was proved to be homogeneous by ultracentrifugation and polyacrylamide gel electrophoresis. D-Erythrulose reductase was active specifically with D-erythrulose as a substrate in the presence of NADH as well as NADPH as a coenzyme, and catalyzed the reduction of D-erythrulose, yielding erythritol as the product. Attempts to demonstrate reversibility of the reaction were unsuccessful. NADH was less effective than NADPH and the Km value for NADH (2.22×10−4M) was much larger than that for NADPH (6.8 × 1O−6M). The molecular weight of D-erythrulose reductase was estimated to be 90,000±1,000 by Sephadex G-200 gel filtration, sedimentation equilibrium analysis and sucrose density gradient centrifugation, and that of its subunit was estimated to be 22,000±5OO by SDS-polyacrylamide gel electrophoresis. The isoelectric point of the enzyme was determined to be pH 6.75 by Ampholine isoelectric focusing. D-Erythrulose reductase was inactivated by exposure to low temperatures. This cold inactivation was at least partially reversible by simply rewarming, and protection against cold inactivation was afforded by NADP+ at low concentrations. NAD+, ATP and other compounds with structures related to that of NADP+ did not exert protection.

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