Isao Umemura

Organization and evolution of variable region genes of the human immunoglobulin heavy chain

We have isolated 23 different cosmid clones of the heavy-chain variable region genes (VH) of human immunoglobulin. These clones encompass about 1000 X 10(3) base-pairs of DNA containing 61 VH genes. Characterization of the 23 clones by Southern blot hybridization showed that VH genes belonging to different families were physically linked in many regions. Cluster 71, which was analyzed in detail, comprised seven VH segments arranged in the same orientation with different intervals. This clone contained internal homology regions, each carrying two VH segments of different families. Comparison of the nucleotide sequences of VH segments within each family showed that profiles of accumulation of mutations in framework (FR) and complementarity-determining (CDR) regions were different. CDR had more mutations at amino-acid-substituting positions than at silent positions, whereas FR had the reverse distribution of mutations. Five out of seven VH segments of this cluster were pseudogenes containing various mutations. VH pseudogenes were classified into two distinct groups; one with a few replacement mutations (conserved pseudogenes), and the other with rather extensive mutations (diverged pseudogenes). The possibility that conserved pseudogenes serve as a reservoir of VH segments is discussed.

Production of l-alanine from ammonium fumarate using two immobilized microorganisms

SummaryFor the efficient production of l-alanine from ammonium fumarate using the aspartase activity of immobilized Escherichia coli cells and l-aspartate β-decarboxylase activity of immobilized Pseudomonas dacunhae cells, alanine racemase and fumarase activities should be eliminated. We investigated various procedures to eliminate these side reactions, and found that both activities of intact E. coli cells could be eliminated by treating the culture broth at pH 5.0 and 45° C for 1 h, and those of intact P. dacunhae cells could be eliminated by treating the culture broth at pH 4.75 and 30° C for 1 h. Further, it was confirmed that l-alanine was efficiently produced using these two immobilized pH-treated microorganisms.

Improvement of production of L-aspartic acid using immobilized microbial cells

SummaryIn our laboratory, EAPc-7 a strain having higher aspartase activity was derived from Escherichia coli ATCC 11303. For the improvement of l-aspartic acid productivity using EAPc-7 cells immobilized in χ-carrageenan, it was necessary to eliminate the fumarase activity which converts fumaric acid to l-malic acid. Several treatments for specifically eliminating fumarase activity from EAPc-7 cells were tested and it was found that when EAPc-7 cells were treated in a culture broth (pH 4.9) containing 50 mM l-aspartic acid at 45° C for 1 h, fumarase activity was almost completely eliminated without inactivation of the aspartase.The treated cells, immobilized in χ-carrageenan, were used for continuous production of l-aspartic acid from ammonium fumarate. The formation of l-malic acid was negligible and the half-life of the immobilized preparation was 126 days.Productivity of immobilized preparation of treated EAPc-7 cells in l-aspartic acid production was six times of that of the parent cell preparation.

Spontaneous R-parity breaking in a supersymmetric majoron model

Abstract Spontaneous R -parity breaking is investigated in a supersymmetric majoron model, where the superfields of antineutrinos and an L = 2 singlet are added to the minimal supersymmetric standard model. The analysis is made by considering the effects of renormalization group evolution of the coupling parameters. It is found that for a certain region of the initial parameters at some unification scale, e.g. ∼ 10 16 GeV, the desired values of the coupling parameters are reproduced at the electroweak scale ∼ 100 GeV to cause spontaneous R -parity breaking. The masses and decays of the light neutrinos are also examined briefly.

First order phase transition in the singlet majoron model

Abstract We investigate the phase transition associated with the electroweak and lepton number symmetry breaking in the singlet majoron model. We find that for a region of the model parameters the first order phase transition occurs, while the Higgs particle mass is larger than 50 GeV.

Neutrinos in the supersymmetric singlet majoron model

Abstract Implications of the spontaneous lepton-number/R-parity violation are investigated in the supersymmetric singlet majoron model, by giving attention to the neutrino properties and the related issues. The neutrino mass spectrum may exhibit a hierarchy, mve ⪡ mvμ ⪡ mvτ, for a specific choice of the coupling parameters, which corresponds to the approximate global symmetries for the conservations of the respective ordinary lepton flavors. The lifetime of the neutrino decay vj → viJ is estimated roughly to be πv ∼ 109 s · (mvi/100 eV)−1 (mvj/100 keV)−4 for mvj>mvj. Then, a detailed numerical analysis is performed on the neutrino masses, mixing and lifetimes to confirm these order estimates, in particular, for the case of vπ with a mass ∼ 10 keV−10 MeV. The experimental constraints derived from some relevant processes involving the massive neutrinos can actually be satisfied there. The results are further compared with a variety of constraints which are placed by the astrophysical and cosmological considerations on the neutrinos and majoron. Some experimental signatures for the lepton-number/R-parity violation are also discussed.

d-Alanine production from dl-alanine by Candida maltosa with asymmetric degrading activity

SummaryTo develop a practical process for d-alanine production from dl-alanine, we screened 107 yeasts for their asymmetric degrading activity against dl-alanine. Candida maltosa JCM1504 degraded the l-isomer ten times more rapidly than the d-isomer. The cells of this strain were used as a biocatalyst for eliminating the l-isomer. However, when the degradation reaction was conducted in the presence of a high concentration of dl-alanine, the pH of the reaction mixture was rapidly increased by the liberation of ammonia from l-alanine, and consequently the reaction stopped. This hindrance was overcome by controlling the pH value at 6.0 with H2SO4 during the reaction. Additionally, we found that the maximum rate of l-isomer degradation was obtained at 30° C and pH 6.0 under conditions of high aeration (1.0 vvm) and agitation (1200 rpm). Under the optimal conditions, the l-isomer of 200 g dl-alanine/l was completely degraded within 40 h and 90 g d-alanine/l remained in the reaction mixture. d-Alanine was easily isolated from the reaction mixture. The chemical and optical purity of the d-isomer product so obtained was 99.0% and 99.9% enantiomeric excess, respectively.

Constraints on the electroweak phase transition in the singlet majoron model

Abstract The phase transition in the singlet majoron model is investigated, which occurs at the temperature of the electroweak scale associated with the spontaneous breakdown of electroweak gauge symmetry and global lepton-number conservation. A parameter region is, in particular, considered where significant one-loop corrections are provided to the effective potential. Then, the first order phase transition may be strong enough to satisfy the constraint from the survival of baryon number asymmetry, while a large enough mass is available for the Higgs particle.

SU(7) GUT and evasion of the survival hypothesis

Abstract Characteristic features of an SU(7) GUT are discussed, in which the fundamental representation 7 consists of SU(5)′ 5 and its two singlets with charge q = ± 1 2 . The so-called survival hypothesis for fermions is naturally evaded by a kind of electric charge conservation due to q = ± 1 2 , and a brief comment on the suppression of the ν el mass is given also.

Dynamical generation of hierarchy in GUTs with softly broken supersymmetry

Abstract Characteristic aspects of Dimopoulos-Georgis mechanism for the hierarchy are investigated in a “semi-realistic” SU(5) model by employing the renormalization group method. The hierarchy is really generated in a “sick” theory by quantum resuscitation without any fine tuning of the coupling constants at M W ≈ 10 2 GeV . It can also be realized in a “normal” theory by choosing the coupling constants suitably. In the latter case, the effective potential has two minima at X = 0 and M G . Some suggestions are presented for constructing a realistic model.