No abstract

Methionine sulfoxide reductase (Msr) catalyzes the thioredoxin-dependent reduction and repair of methionine sulfoxide (MetO). Although Msr genes are not present in most hyperthermophile genomes, an Msr homolog encoding an MsrA-MsrB fusion protein (MsrAB Tk ) was present on the genome of the hyperthermophilic archaeon Thermococcus kodakaraensis. Recombinant proteins corresponding to MsrAB Tk and the individual domains (MsrA Tk and MsrB Tk ) were produced, purified, and biochemically examined. MsrA Tk and MsrB Tk displayed strict substrate selectivity for Met-S-O and Met-R-O, respectively. MsrAB Tk , and in particular the MsrB domain of this protein, displayed an intriguing behavior for an enzyme from a hyperthermophile. While MsrAB Tk was relatively stable at temperatures up to 80°C (with a half-life of ϳ30 min at 80°C), a 75% decrease in activity was observed after 2.5 min at 85°C, the optimal growth temperature of this archaeon. Moreover, maximal levels of MsrB activity of MsrAB Tk were observed at the strikingly low temperature of 30°C, which also was observed for MsrB Tk . Consistent with the low-temperature-specific biochemical properties of MsrAB Tk , the presence of the protein was greater in T. kodakaraensis cells grown at suboptimal temperatures (60 to 70°C) and could not be detected at 80 to 90°C. We found that the amount of intracellular MsrAB Tk protein increased with exposure to higher dissolved oxygen levels, but only at suboptimal growth temperatures. While measuring background rates of the Msr enzyme reactions, we observed significant levels of MetO reduction at high temperatures without enzyme. The occurrence of nonenzymatic MetO reduction at high temperatures may explain the specific absence of Msr homologs in most hyperthermophiles. Together with the fact that the presence of Msr in T. kodakaraensis is exceptional among the hyperthermophiles, the enzyme may represent a novel strategy for this organism to deal with low-temperature environments in which the dissolved oxygen concentrations increase.Reactive oxygen species are harmful to the cell by oxidizing various cell components, such as lipids, nucleic acids, and proteins. Among the amino acids, methionine (Met) residues are known to be particularly susceptible to oxidative stress and are easily oxidized to methionine sulfoxides (MetO). Methionine sulfoxide reductase (Msr) is an enzyme that repairs the oxidized methionine and catalyzes the thioredoxin-dependent reduction of MetO to Met (6). The oxidation of Met results in the formation of two asymmetric molecules, Met-S-O and Met-R-O. Each MetO is reduced by a specific and structurally distinct enzyme: Met-S-O is reduced by MsrA, and Met-R-O is reduced by MsrB. Msr proteins are considered to play vital roles in maintaining the intracellular redox balance and in the repair of oxidized proteins (5, 9). In mammals, defects in the function of Msr have been reported to result in neurological disorders and, in some cases, a decrease in life span (30,31).Although structurally distinct, MsrA and MsrB ...

No abstract

In the rape or "Seiyo-Undai"1) (B. Napella) field, there are found in places a certain type of highly sterile individuals . Such individ uals can be easily detected among the normal in the end of flower season owing to their continuous and successive blooming. In 1927 the authors collected some seeds from those sterile individuals, and the offspring-tests were made for two generations in which, contrary to expectation, no sterile plants appeared. Thus the problem has lost its interest and the authors' attention has not been paid for years to this sterile type. In the spring of 1933, however, an idea , oc curred to the authors, that such spontaneous, highly sterile individ uals might be haploids which produce diploid offspring. Closer in vestigations proved this supposition to be correct. This is the first known case of haploid plants in Brassica. NOGUCHI's report (2) treat ing maternal hybrid has often been misquoted in this connection. In the rape field otherr types of sterility were also met with. Among those especially a type with a higher number of chromosomes than the normal attracted the authors' attention.The haploid mutant: Plants of this type of sterility occur in the field far more than those of the other types. The leaves and flowers are obviously smaller than those of diploid in the same line. Though the plant is generally lower in hight than the diploid, it may surpass the latter in bight , on account of its continuous development of inflorescences. The epidermal cell of the haploid was, in a few individuals examined, markedly smaller than that of the diploid. Half

No abstract