PURIFICATION AND CHARACTERIZATION OF AN NADP ⁺ ‐LINKED ALCOHOL OXIDO‐REDUCTASE WHICH CATALYZES THE INTERCONVERSION OF γ‐HYDROXYBUTYRATE and SUCCINIC SEMIALDEHYDE¹

Abstract

Abstract— An NADP+ ‐linked enzyme, capable of interconverting γ‐hydroxybutyrate and succinic semialdehyde, has been isolated from hamster liver and brain. The enzyme which was isolated from liver has been purified 300‐fold and exhibits a single band by polyacrylamide gel electrophoresis. The molecular weight of the enzyme is ‐ 31,000 as estimated from gel filtration and 38,000 as estimated from sodium dodccyl sulfate gel electrophoresis. The enzyme is inhibited by amobarbital, diphenylhy‐dantoin, 2‐propylvalerate, and diethyldithiocarbamate, but not by pyrazole. The enzymes from brain and liver appear to be very similar with regard to their molecular weights and their kinetic constants for γ‐hydroxybutyrate and succinic semialdehyde.

Regulation of Glucagon Secretion in Normal and Diabetic Human Islets by γ-Hydroxybutyrate and Glycine

“…As a consequence of GABA metabolism, SSA produced via GABA transaminase enters the TCA cycle through SSA dehydrogenase. In the central nervous system, a fraction of SSA is diverted to GHB via the NADPHdependent SSA reductase (38). GHB, a potent inhibitory neurotransmitter, is then converted back to SSA via the NAD-dependent GHB dehydrogenase (GHBDH) to form the "GHB loop" (39 -41).…”

An overview of ?-hydroxybutyrate catabolism: The role of the cytosolic NADP+-dependent oxidoreductase EC 1.1.1.19 and of a mitochondrial hydroxyacid-oxoacid transhydrogenase in the initial, rate-limiting step in this pathway

“…Two unusual oxidoreductases, one cytosolic (19) and the other mitochondrial (20), that catalyze the oxidation of GHB to SSA have now been isolated. The cytosolic enzyme, which will be referred to as GHB-dehydrogenase in this review, was first purified to homogeneity from hamster liver (19) and was found to be an NADP+-dependent oxidoreductase. A study of the substrate specificity of purified GHB-dehydrogenase revealed that o-glucuronate and L-gulonate, the product of D-glucuronate reduction, were also good substrates (19).…”

“…The cytosolic enzyme, which will be referred to as GHB-dehydrogenase in this review, was first purified to homogeneity from hamster liver (19) and was found to be an NADP+-dependent oxidoreductase. A study of the substrate specificity of purified GHB-dehydrogenase revealed that o-glucuronate and L-gulonate, the product of D-glucuronate reduction, were also good substrates (19). The physical characteristics, as well as the substrate and inhibitor specificity of this enzyme, indicate that the ability to catalyze the oxidation of GHB probably represents a previously unreported activity for the NADP+-dependent oxidoreductase (EC 1.1.1.19) commonly known as Dglucuronte reductase (21).…”

“…The reaction mixture contains 10 mM GHB, 1.0 mM D-glucuronate, 0.1 mM NADP § 80 mM phosphate buffer, pH 7.6, enzyme and sufficient water to bring the volume to 1.0 ml. SSA and NADPH were determined as previously described (19).…”

Formation Pathways of γ-Butyrolactone from the Furan Ring of Tegafur during Its Conversion to 5-Fluorouracil

“…We observed similar results during the formation of GBL/GHB in the hepatic S9, which indicates that the CYP2A6-mediated metabolic pathway of the furan ring of FT, followed by the sequential conversion of SA to GBL/GHB may contribute mainly to the formation of GBL/GHB under physiological conditions. The studies on endogenous GBL/ GHB catabolism have shown the oxidation of GBL/GHB to succinic semialdehyde by GHB dehydrogenase, followed by its oxidation to succinate by succinic semialdehyde dehydrogenase in mitochondria (Kaufman et al, 1979). Therefore, GBL/GHB generated after the administration of FT may be finally metabolized to succinate in mitochondria in vivo.…”