UDP-glucuronosyltransferases 1A6 and 1A10 catalyze reduced menadione glucuronidation

Menadione (2-methyl-1,4-naphthoquine), also known as vitamin K3, has been widely used as a model compound in the field of oxidative stress-related research. The metabolism of menadione has been studied, and it is known that menadione undergoes a two-electron reduction by NAD(P)H:Quinone oxidoreductase 1 (NQO1) after which the reduced form of menadione (2-methyl-1,4-naphthalenediol, menadiol) is glucuronidated and excreted in urine. To investigate which human UDP-glucuronosyltransferase (UGT) isoforms participate in the glucuronidation of menadiol reduced by NQO1 from menadione, we first constructed heterologously expressed NQO1 in Sf9 cells and tested the menadiol glucuronidating activity of 16 human recombinant UGT isoforms. Of the 16 UGT isoforms, UGTs 1A6, 1A7, 1A8, 1A9, and 1A10 catalyzed menadiol glucuronidation, and, of these, UGTs 1A6 and 1A10 catalyzed menadiol glucuronidation at much higher rates than the other UGTs. Menadiol was regioselectively glucuronidated in the manner of 4-position > 1-position by UGTs 1A7, 1A8, 1A9, and 1A10. In contrast to these UGTs, only UGT1A6 exhibited 1-menadiol-preferential glucuronidating activity. The results suggest possible detoxification pathways for quinones via NQO1 reduction followed by UGT glucuronidation.     

Expression of human leukotriene A4 hydrolase cDNA in Escherichia coli

The cDNA clone encoding human leukotriene A4 hydrolase was inserted into a vector pUC9 and expressed in Escherichia coli as a fusion protein containing the first 10 amino acid residues derived from a vector. The leukotriene A4 hydrolase activity was recovered in the soluble fraction of the transformants. The purified enzyme showed kinetic properties similar to the native enzyme, including inactivation by the substrate and sulfhydryl-modifying reagents. The results demonstrate that a protein with an Mr of 70,000 was expressed in Escherichia coli with a full enzyme activity and structural fidelity. Acquisition of the expression system makes it feasible to elucidate the reaction mechanism of the enzyme.     

GPI1 stabilizes an enzyme essential in the first step of glycosylphosphatidylinositol biosynthesis.

Attachment of glycosylphosphatidylinositol (GPI) is essential for the surface expression of many proteins. Biosynthesis of glycosylphosphatidylinositol is initiated by the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol. In mammalian cells, this reaction is mediated by a complex of PIG-A, PIG-H, PIG-C, and GPI1. This complexity may be relevant for regulation and for usage of a particular phosphatidylinositol. However, the functions of the respective components have been unclear. Here we cloned the mouse GPI1 gene and disrupted it in F9 embryonal carcinoma cells. Disruption of the GPI1 gene caused a severe but not complete defect in the generation of glycosylphosphatidylinositol-anchored proteins, indicating some residual biosynthetic activity. A complex of PIG-A, PIG-H, and PIG-C decreased to a nearly undetectable level, whereas a complex of PIG-A and PIG-H was easily detected. A lack of GPI1 also caused partial decreases of PIG-C and PIG-H. Therefore, GPI1 stabilizes the enzyme by tying up PIG-C with a complex of PIG-A and PIG-H.     

Purification of Clostridium botulinum Type F Progenitor Toxin

Clostridium botulinum type F progenitor toxin was purified to a homogeneous state as judged by gel filtration on Sephadex G-200, ultracentrifugation, and disc electrophoresis. The sedimentation constant, corrected to water at 20 C, of type F progenitor toxin was determined to be 10.3 and the molecular weight to be 235,000 by ultracentrifugation at pH 6.0. The purified toxin contained a toxicity of 1.2 x 10(8) 50% lethal doses/mg of N. In agar gel double diffusion, it formed two precipitin lines at pH 6.0. The progenitor toxin of type F differs from that of type A in that it contains no hemagglutinin and from that of type E in that it is not activable.