Eizoh Nagahisa

Presence of Free D-Amino Acids in Microalgae

Several species of microalgae (phytoplankton), 4 species of freshwater algae and 4 species of marine diatoms, were cultured germ-free in the laboratory. The presence of free D-amino acids was verified in these species by a reversed-phase HPLC analysis. D-Aspartate was detected in all the microalgae examined, but D-alanine was only present in the marine diatoms. The D-amino acid content in Asterionella sp. of the marine diatoms increased from the exponential phase to the stationary phase and then decreased to the phase of decline.

A simple and rapid method for the analysis of fish histamine by paper electrophoresis

The described analytical method for histamine determination in fish and seafood consists of sample extraction, adsorption onto a paper disc, application of the paper disc onto electrophoresis paper, electrophoresis for only 10 min, drying, and color developing by Pauly’s reagent. Histamine can be satisfactorily detected and completely separated from histidine, carnosine and other Pauly reagent-positive compounds. This method does not require expensive instrumentation and any tedious pretreatment to eliminate potential interference by other imidazole compounds, such as histidine or carnosine. This method can be used to detect histamine in multiple fish and seafood samples simultaneously that contain as little as 15 p.p.m. histamine (1.5 mg/100 g).

Occurrence of β-alanine-specific opine dehydrogenase in the muscle of the limpet Cellana grata Gould (Archaeogastropoda)

The muscular tissues of the limpet Cellana grata exhibited beta-alanopine dehydrogenase (beta-AlDH) activity in addition to tauropine dehydrogenase (TaDH) activity and weak lactate dehydrogenase activity. Opine dehydrogenases (OpDHs) were purified, and two different types of OpDH, i.e. TaDHs and OpDHs showing beta-AlDH activity, were isolated. From the specificity for amino acid and opine, OpDHs showing beta-AlDH activity were concluded to be a true beta-AlDH showing strict substrate specificity for beta-alanine. Although the catalytic properties of beta-AlDH and TaDH were essentially similar, they were distinct from each other with respect to the amino acid substrate specificity and the K(m) values. Apparent K(m) values (mM) for the preferred amino acid substrate, pyruvate, NADH, the preferred opine substrate, and NAD+ were: 14.3 (beta-alanine), 0.19, 0.032, 35.2 (beta-alanopine), and 0.78 for beta-AlDH; and 33.3 (taurine), 0.53, 0.076, 48.6 (tauropine), and 0.58 for TaDH, respectively. Great similarities were found between beta-AlDH and TaDH with respect to molecular properties: molecular masses (both enzymes were monomeric proteins of approximately 40,000 Da), amino acid compositions, and N-terminal amino acid sequences (30 amino acid residues were identical). Partial similarities were also recognized between their lysyl endopeptidase maps. These results clearly show that beta-alanine-specific OpDH, a true beta-AlDH, is present in the limpet muscle.

Alanine racemase activity in the microalga thalassiosira sp.

In this paper, the authors report the detection of alanine racemase activity in the marine diatom Thalassiosira sp. Since the Thalassiosira sp. was cultured under germ-free conditions, it appeared that D-alanine was not derived from bacteria but was produced through catalysis by algal alanine racemase. The rate of conversion of L-alanine to D-alanine was approximately the same as that for the reverse reaction, and the enzyme catalyzed the equilibration of the D- and L-forms. The crude enzyme preparation obtained from the cells at the stationary phase of the growth cycle had an optimal pH of approximately 9.5. The Lineweaver—Burk analysis showed that the Km for D- and L-alanine was 16.5 mM and 29.4 mM, respectively. It appears that the enzyme is highly specific for D- or L-alanine because it does not catalyze the racemization of other amino acids. In addition, after gel filtration, the enzyme did not require exogenous pyridoxal 5′-phosphate (PLP) for its activity, however, the effects of several chemicals suggest that the enzyme may be PLP-dependent. The enzyme is more similar to that found in invertebrates when compared with that found in bacteria. This is the first report on the occurrence of alanine racemase activity in the microalga Thalassiosira sp.

Tauropine dehydrogenase from the starfish Asterina pectinifera (Echinodermata: Asteroidea): presence of opine production pathway in a deuterostome invertebrate.

Tauropine dehydrogenase (tauropine:NAD oxidoreductase; TaDH) was purified to homogeneity from the body wall of the starfish Asterina pectinifera Müller at Troschel(Echinodermata: Asteroidea) by means of (NH4)2SO4 precipitation followed by column chromatographies in DEAE-cellulose, Sephadex G75, Macro-prep ceramic hydroxyapatite, PBE 94, and Toyopearl HW50S. The enzyme was a monomeric protein of approximately 42000 Da and pI 5.2. The maximum rate of the tauropine biosynthetic reaction was observed at pH 6.0, and that of the tauropine catabolic reaction was at pH 8.7-9.2. Taurine and pyruvate were the preferred substrates. The tauropine catabolic reaction was inhibited by the substrate tauropine: the peak rate was observed at 12.5 mM. Apparent Km values for NADH, taurine, and pyruvate were 0.036 +/- 0.002, 21.3 +/- 1.6, and 0.46 +/- 0.02 mM, respectively, and for tauropine and NAD+ were 2.64 +/- 0.73 and 0.068 +/- 0.005 mM, respectively. The molecular and catalytic properties of the starfish TaDH were basically similar to those of TaDH from other species belonging to the lower invertebrate phyla and the middle phyla of Prostostomia. Tauropine accumulation in vivo during experimental anoxia was also demonstrated. These results gave clear evidence of opine production pathway in deutrostome invertebrate.

Purification and some properties of alanine racemase from the marine gastropod Cellana grata

High levels of free D-alanine were found in the muscle of a marine gastropod Cellana grata that inhabited the intertidal zone, and alanine racemase activity was detected in the muscle. The authors purified alanine racemase from the muscle of C. grata to characterize its enzymological properties. The molecular mass of the enzyme was estimated to be 40.5 kDa by sodium dodecylsulfatepolyacrylamide gel electrophoresis and 41.4 kDa by gel filtration, suggesting that the enzyme was monomeric in nature. Kinetic experiments, performed using the purified enzyme, revealed that the Lineweaver-Burk plot for D-alanine as a substrate resulted in a Km value of 20.4 mM, and the value for L-alanine was 43.0 mM. Of the several types of amino acids tested, alanine was found to be the specific substrate for the enzyme. In the measurement of alanine racemase activity, exogenous pyridoxal 5′-phosphate (PLP) was not required for the enzyme activity; however, aminooxyacetic acid, hydroxylamine and phenylhydrazine, which inhibit PLP-dependent enzymes, strongly inhibited the enzyme activity. These results suggest that the enzyme is PLP-dependent. This is the first report on the purification and some properties of alanine racemase in a marine gastropod.