Properties of aspartate racemase, a pyridoxal 5'-phosphate-independent amino acid racemase.

Aspartate racemase from Streptococcus thermophilus contains no pyridoxal 5'-phosphate or other cofactors such as FAD, NAD+, and metal ions. It was affected by neither carbonyl reagents such as hydroxylamine nor sodium borohydride but was strongly inhibited by iodoacetamide and other thiol reagents. Aspartate, cysteate, and cysteine sulfinate were the only substrates. The Km values for L- and D-aspartate were 35 and 8.7 mM, respectively. The enzyme catalyzed the exchange of alpha-hydrogen of the substrate with the solvent hydrogen. Racemization of L-aspartate in 2H2O showed an overshooting in the optical rotation of aspartate before the substrate was fully racemized. This shows that the removal of alpha-hydrogen of the substrate is at least partially rate-determining. When L- or D-aspartate was incubated with aspartate racemase in tritiated water, tritium was incorporated preferentially into the product enantiomer. The results strongly suggest that aspartate racemase contains two hydrogen acceptors.     

Regulation and evolution of chlorophyll metabolism

Chlorophylls are the most abundant tetrapyrrole molecules essential for photosynthesis in photosynthetic organisms. After many years of intensive research, most of the genes encoding the enzymes for the pathway have been identified, and recently the underlying molecular mechanisms have been elucidated. These studies revealed that the regulation of chlorophyll metabolism includes all levels of control to allow a balanced metabolic flow in response to external and endogenous factors and to ensure adaptation to varying needs of chlorophyll during plant development. Furthermore, identification of biosynthetic genes from various organisms and genetic analysis of functions of identified genes enables us to predict the evolutionary scenario of chlorophyll metabolism. In this review, based on recent findings, we discuss the regulation and evolution of chlorophyll metabolism.     

Precise localization of the human thyroxine-binding globulin gene to chromosome Xq22.2 by fluorescence in situ hybridization

The human thyroxine-binding globulin (TBG) gene has been localized to X chromosome (Xq22.2) by in situ hybridization using a biotinylated gDNA probe. This is consistent with previous mapping of the TBG gene to chromosome Xq21-q22.     

The Schizosaccharomyces pombe cdc6 gene encodes the catalytic subunit of DNA polymerase δ

The cdc6 mutants of Schizosaccharomyces pombe have been classified as being defective in progression through the G2 phase of the cell cycle. We cloned an S. pombe gene that could complement the temperature-sensitive growth of the cdc6-23 mutant. Unexpectedly, the cloned gene was allelic to pol3, which encodes the catalytic subunit of DNA polymerase δ. Integration mapping confirmed that cdc6 and pol3 are identical. The cdc6-23 mutant carries one amino acid substitution in the conserved N3 region of Pol3. Received: 17 October 1996 / Accepted: 19 November 1996     

Antibacterial activity of disodium succinoyl glycyrrhetinate,a derivative of glycyrrhetinic acid against Streptococcus mutans

Streptococcus mutans is a cariogenic bacterium that localizes in the oral cavity. Glycyrrhetinic acid (GRA) is a major component of licorice extract. GRA and several derivatives, including disodium succinoyl glycyrrhetinate (GR‐SU), are known to have anti‐inflammatory effects in humans. In this study, the antimicrobial effect of GRA and its derivatives against the S. mutans UA159 strain were investigated. Minimum inhibitory concentrations (MICs) of GRA and GR‐SU showed antibacterial activity against the S. mutans strain, whereas other tested derivatives did not. Because GR‐SU is more soluble than GRA, GR‐SU was used for further experiments. The antibacterial activity of GR‐SU against 100 S. mutans strains was evaluated and it was found that all strains are susceptible to GR‐SU, with MIC values below 256 µg/mL. A cell viability assay showed that GR‐SU has a bacteriostatic effect on S. mutans cells. As to growth kinetics, sub‐MICs of GR‐SU inhibited growth. The effect of GR‐SU on S. mutans virulence was then investigated. GR‐SU at sub‐MICs suppresses biofilm formation. Additionally, GR‐SU greatly suppresses the pH drop caused by the addition of glucose and glucose‐induced expression of the genes responsible for acid production (ldh and pykF) and tolerance (aguD and atpD). Additionally, expression of enolase, which is responsible for the carbohydrate phosphotransferase system, was not increased in the presence of GR‐SU, indicating that GR‐SU suppresses incorporation of sugars into S. mutans. In conclusion, GR‐SU has antibacterial activity against S. mutans and also decreases S. mutans virulence.     

Differences in rapid eye movement sleep behavior disorder manifestation between synucleinopathies and tauopathies

Rapid eye movement sleep behavior disorder (RBD) frequently occurs in synucleinopathies including multiple system atrophy, Parkinson’s disease, and dementia with Lewy bodies despite the clinical course of RBD being different between these disorders. Comparatively, the existence of RBD symptoms is relatively rare in patients with progressive supranuclear palsy, a tauopathy showing atypical parkinsonism compared with Parkinson’s disease. Moreover, in patients with Alzheimer’s disease, which is another tauopathy, RBD symptoms are less frequent than dementia with Lewy bodies, although both disorders share commonalities in terms of the existence of cortical dementia. Thus, RBD is thought to be relatively specific to synucleinopathies.

     

Thermostable phenylalanine dehydrogenase of Thermoactinomyces intermedius: cloning, expression, and sequencing of its gene

The gene encoding the thermostable phenylalanine dehydrogenase [EC 1.4.1.-] of a thermophile, Thermoactinomyces intermedius, was cloned and its complete DNA sequence was determined. The phenylalanine dehydrogenase gene (pdh) consists of 1,098 nucleotides and encodes 366 amino acid residues corresponding to the subunit (Mr 41,000) of the hexameric enzyme. The amino acid sequence deduced from the nucleotide sequence of the pdh gene of T. intermedius was 56.0 and 42.1% homologous to those of the phenylalanine dehydrogenases of Bacillus sphaericus and Sporosarcina ureae, respectively. It shows 47.5% homology to that of the thermostable leucine dehydrogenase from B. stearothermophilus. The pdh gene was highly expressed in E. coli JM109, the amount of phenylalanine dehydrogenase produced amounting up to about 8.3% of that of the total soluble protein. We purified the enzyme to homogeneity from transformant cells in a day, with a 58% recovery.     

Association between light exposure at night and manic symptoms in bipolar disorder: cross-sectional analysis of the APPLE cohort

ABSTRACT

Previous studies have found that keeping the room dark at night was associated with a decrease in manic symptoms for patients with bipolar disorder (BD). However, the association between light at night of real-life conditions and manic symptoms is unclear. We investigated the association between bedroom light exposure at night and manic symptoms in BD patients. One-hundred and eighty-four outpatients with BD participated in this cross-sectional study. The average light intensity at night during sleep was evaluated using a portable photometer for seven consecutive nights. Manic symptoms were assessed using the Young Mania Rating Scale (YMRS), and scores ≥5 were treated as a “hypomanic state.” The median (interquartile range) YMRS score was 2.0 (0–5.0), and 52 (28.2%) participants were in a hypomanic state. The prevalence of a hypomanic state was significantly higher in the participants with an average light intensity at night exposure of ≥3 lux than in those with <3 lux (36.7% versus 21.9%; P = .02). In multivariable logistic regression analysis adjusted for BD type, depressive symptoms, sleep duration, and daytime physical activity, the odds ratio (OR) for a hypomanic state was significantly higher for the participants with an average light intensity at night exposure of ≥3 lux than for those with <3 lux (OR: 2.15, 95% confidence interval: 1.09–4.22, P = .02). This association remained significant at the cutoff value of YMRS score ≥6 (OR: 2.51, 95% confidence interval: 1.15–5.46; P = .02). The findings of this study indicate bedroom light exposure at night is significantly associated with manic symptoms in BD patients. Although the results of this cross-sectional investigation do not necessarily imply causality, they may serve to inform beneficial nonpharmacological intervention and personalized treatment of BD patients.