Reduction properties of nitrated naphthalenes: relationship between electrochemical reduction potential and the enzymatic reduction by microsomes or cytosol from rat liver.

The nitroreductase activities of rat liver microsomes and cytosol towards various nitrated naphthalenes (1-, 2-mononitro-, 1,3-, 1,5-, 1,7-, 1,8-dinitro-1,3,5- and 1,3,8-trinitronaphthalenes) were characterized as follows. (1) The rates of reduction of nitrated naphthalenes in either microsomal or cytosolic incubation were found to increase in the order of trinitro- > dinitro- > mono-nitronaphthalene, although, in the case of microsomal nitroreduction, trinitronaphthalenes were reduced more rapidly than in cytosol. (2) The effective cofactors, electron donors, in the nitroreduction of nitrated naphthalenes in cytosol were NADH and hypoxanthine, but not NADPH. (3) The nitrated naphthalenes with a nitro group at a beta-position appear to be more easily reduced among the various isomers. The cytosolic nitroreductase activities towards the nitrated naphthalenes were closely related to the single-electron reduction potentials measured by cyclic voltammetry and hence, there was a good relationship between the logarithm of nitroreductase activities and the electrochemical reduction potentials. In microsomes, nitroreductase activities were rather less well related to electrochemical reduction potentials.     

Marked Alteration at Midblastula Transition in the Effect of Lithium on Formation of the Larval Body Pattern of Xenopus laevis

Embryos of Xenopus laevis were exposed to 0.4 M LiCl for 5 min at various stages of development. The effect of lithium on the larval body pattern could be detected from the 2-cell to the late gastrula stage, but changed from reduction of posterior structures ("anteriorization") to reduction of anterior structures ("posteriorization") just after the 12th cleavage, the time of midblastula transition (MBT). Temporal coincidence of MBT with alteration of the effect of lithium was observed even with embryos derived from half-egg fragment, in which MBT occurs just after the 11th cleavage. These results suggest the existence of a mechanism for formation of the basic plan of the larval body whose function changes at MBT. Combinations of the pre- and post-MBT exposures to lithium induced marked posteriorization in most larvae, indicating that the basic plan is not irreversibly determined until MBT, but is fixed during post-MBT stages.     

Comparative studies on induction and rejoining of DNA single-strand breaks by radiation and chemical carcinogen in mammalian cells in vitro

This study, using the 5–20% alkaline sucrose gradient method, indicated that single-strand breaks of DNA in cultured mammalian cells were induced as a linear function of the dose of X-ray and chemical carcinogen (4-HAQO). The rejoining of broken single-strand of DNA induced by these agents seems to consist of two processes: an initial rapid rejoining process and a late slow rejoining process. Single-strand breaks of cellular DNA induced by these two agents rejoin at nearly the same rate for each of the two processes during incubation.     

The Involvement of Indole-3-Acetic Acid Produced by Bradyrhizobium elkanii in Nodule Formation

IAA-deficient mutants T10, T27 and TN3 were isolated from B.elkanii USDA 31 by spontaneous and/or N-methyl-N'-nitro-N-nitrosoguanidine(NTG) mutageneses. Inoculation with these mutants significantlyreduced the nodule number on soybean roots when compared tothat of the parent strain. Furthermore, exogenous IAA applicationrestored the nodule number of soybeans inoculated with TN3 tothe original level. (Received July 18, 1994; Accepted September 13, 1994)     

The VIG9 gene products from the human pathogenic fungi Candida albicans and Candida glabrata encode GDP-mannose pyrophosphorylase

We have identified two genomic DNA fragments from the human pathogenic fungi, Candida albicans (CaVIG9) and Candida glabrata (CgVIG9) that encode GDP-mannose pyrophosphorylase, a key enzyme for protein glycosylation. The VIG9 homologues of CaVIG9 and CgVIG9 complement an identified protein glycosylation-defective mutation, vig9, of Saccharomyces cerevisiae. The nucleotide sequences of the ORFs, which are 83 and 90% identical to that of the ScVIG9 protein, respectively, showed a predicted gene product homologous to S. cerevisiae GDP-mannose pyrophosphorylase. We examined the enzyme activity of a glutathione S-transferase fusion of each VIG9 gene to synthesize GDP mannose in the cell extracts of a heterologous Escherichia coli expression system. We also developed a method for detecting the enzyme activity using a non-radioactive substrate that would be applicable to high throughput screening.     

Double-stranded RNA-binding protein DRB3 negatively regulates anthocyanin biosynthesis by modulating PAP1 expression in Arabidopsis thaliana

Journal of Plant Research - The model plant Arabidopsis thaliana has five double-stranded RNA-binding proteins (DRB1-DRB5), two of which, DRB1 and DRB4, are well characterized. In contrast, the...