Excitatory amino acid (EAA) receptors are nowadays divided into 2 major categories according to their signal transduction systems. A metabotropic type of EAA receptors is linked to hydrolysis of peculiar phospholipids or formation of cyclic nucleotides, while an ionotropic type is associated with an ion channel permeable to particular cations. The ionotropic receptors are further classified on the basis of differential sensitivity to excitement by the exogenous agonist N-methyl-D-aspartic acid (NMDA). Ionotropic receptors insensitive to NMDA are distinguishable by preference to excitation by the other exogenous agonist α-amino-3-hydroxy-5-methyl-isoxazole-4-propionic or kainic acid. These ionotropic receptors have been analyzed by conventional ligand binding techniques which often meet with critical methodological pitfalls and artifacts. In this review, therefore, our data obtained using accurate and reproducible receptor binding and gel-shift assays will be outlined with respect to signal transduction mediated by EAA from cell membranes to nuclei. Pharmacological evaluation is also discussed on the search for and the development of drugs useful for therapy and treatment of a variety of neurodegenerative disorders associated with dysfunction of EAA receptors.
Various interfacial phenomena in the field of pharmaceutical sciences were investigated. A striking difference was found in the mode of hemolytic action between anionic and cationic surfactants, mainly due to the difference in membrane components with which these two types of hemolytic agent interact in the surface region of erythrocytes. The permeability of microcapsule membranes composed of electrically neutral polymers toward water-soluble solute increased with increasing microcapsule size while that toward sparingly-soluble solute decreased as the microcapsule size increased. In the case of polyelectrolyte microcapsule membranes, which have many dissociable groups, the permeability was found strongly dependent on the pH of the medium. Degradation of poly (L-lactic acid) microcapsules was revealed to start from the surface through electrophoretic mobility measurements, the rate of which was noticeably affected by the pH and ionic strength of the medium and the presence of plasma proteins. Disintegration of polyelectrolyte microcapsules was caused by the action of such fibrous proteins as fibrinogen principally through hydrophobic interaction between the constituent polymers and the protein. An important role of the complement was found in the adhesion of platelets to the surface of negatively charged microcapsules. Microcapsules with different surface potentials were phagocytosed least by phagocytes when they had a surface potential identical with that of the cells. Cell electrophoresis was applied to estimate the charge distribution in the surface region of biological cells and to elucidate the action mechanism of inhalation anesthetics.
The action of neuropeptides at the synapse is terminated through enzymatic degradation by membrane-bound proteases. We defined and purified membrane-bound proteases functioning at the initial stage of degradation of four neuropeptides. 1. Substance P-degrading endopeptidases isolated from the rat brain and pig striatum showed similar properties to those of endopeptidase-24.16 (neurolysin) except for cleavage sites of substance P. 2. LHRH fragment (1-5)-generating endopeptidases isolated from the neuroblastoma cells and rat brain showed similar properties to those of endopeptidase-24.15 (thimet oligopeptidase). 3. One of two dynorphin-degrading cysteine proteases isolated from neuroblastoma cells showed strict specificity toward the Arg-Arg residues. 4. Endopeptidase-24.11 (neprilysin) isolated from the rat brain was identified as a somatostatin-degrading enzyme.
The stability of allantoin was studied in pH 3.0, 6.0, and 8.0 buffer solutions at 50°C for 55 d. Allantoin was determined by high performance liquid chromatography (HPLC) with a cation exchange mode and colorimetry. The known degradation compounds, allantoic acid and glyoxylic acid, were simultaneously determined by ion chromatography. Urea was determined by HPLC with an ion pair mode. In the stability studies on pH 6.0 and 8.0 solutions, new degradation compounds of allantoin were identified as two growing unknown peaks in the HPLC chromatogram. Isolation of these compounds by preparative HPLC and 1H, 15N and 18C-NMR spectra revealed that they were condensates of allantoin and glyoxylic acid, which also reacted positively in phenylhydrazine colorimetry. The amounts of these compounds were calculated from the determination results of other allantoin related compounds in the buffer solutions and were estimated as the biggest amount among all other compound. As they were found to be stable in an alkaline solution, conditions for hydrolysis in the colorimetric determination of allantoin were further examined. It was found that the longer hydrolysis gave more than 90% recovery in the colorimetry.
We studied the effect of selenium on the glycolysis and gluconeogenesis system in the rat liver. Significant decreases in glucose level in the serum were observed from the 4 th day after daily intraperitoneal (i.p.) administration of selenite (173 μg/kg, 78.9 μg/kg of selenium base equivalent). Selenium was also effective in reducing a precursor of gluconeogenesis, lactate, alanine or glycerol, in the serum. Moreover, there were significant decreases in the activities of pyruvate carboxylase and glucose-6-phosphatase, a rate-limiting enzyme of gluconeogenesis, in the liver of selenium-treated rates. On the contrary, the activities of glycokinase and phosphofructokinase, a rate-limiting enzyme of glycolysis, in the liver of rat treated with selenium significantly increased in comparison with the control group. These data, therefore, indicated that the hypoglycemic effect of selenium might be due to the acceleration of glucose metabolism and the inhibition of glucose synthesis in the liver, suggesting a decrease in a source of precursor supply for the gluconeogenesis.
Perchloric acid-soluble fractions (PASFs) were separated, in yields of 87.0-151.9 mg per 1.0 g of wet meconium sample, from six samples of human meconium, and identified as glycoproteins having 41.2-74.1% carbohydrate by chemical composition analysis. Six PASFs reacted with anti-A, -B, -Lea and -Leb sera, but did not react with anti-M and -N sera. These PASFs alos reacted with many lectins such as DBA, UEA-I, Vicia graminea lectin (VGA), Vicia unijuga lectin (VUA), Con A, WGA, RCA-I, PHA-E, SBA, SJA, and influenza A and B viruses. The serological results show that six PASFs contained VGA or VUA-binding (Vgu) glycoproteins as new oncofetal substances, but did not contain M and N blood group substances.