A New Myelin-Deficient Mutant Hamster: Biochemical and Morphological Studies

Biochemical and morphological studies were done on a new trembling mutant hamster CBB. The yield of myelin from the mutant was 30 and 40% of the control at 46 and 140 days of age, respectively, but myelin composition and 2',3'-cyclic nucleotide-3'-phosphohydrolase (CNPase) activity were normal. Morphologically, about 18% of the axons were myelinated in the mutant optic nerve at 46 days of age, in which the myelinated fibers were those with larger diameters (more than 0.6 micron), while the control had a peak at 0.4 micron in diameter. The ultrastructure and thickness of compact myelin lamellae in the mutant were normal. Myelination and the structure of peripheral nerve myelin appeared normal. The results indicate that the essential defect is the delay and arrest of myelination in the CNS, which is probably caused by either a decreased rate of synthesis of myelin components in oligodendrocytes or a defect in the oligodendrocyte-axon recognition in smaller axons.     

4-Hydroxyaminoquinoline 1-oxide metabolism and DNA adducts in the early stage of tumorigenesis in rats: comparison of target organ pancreas with non-target organ liver

In order to probe key early molecular events which might be responsible for the initiation of rat pancreatic tumorigenesis by 4-hydroxyaminoquinoline 1-oxide (4-HAQO), the uptake and metabolism of carcinogen and the formation and subsequent repair of DNA adducts were monitored under conditions of high and low tumorigenicity, respectively in partially pancreatectomized and non-operated animals, and in the liver, a non-target organ for this carcinogen. Although uptake of radioactively labelled 4-HAQO was higher in the liver than in the pancreas, generation of DNA adducts was 20 times greater in the latter organ. This discrepancy was probably due to a difference in the metabolic profile of 4-HAQO. The spectrum of the adducts was qualitatively similar in both organs. No qualitative or quantitative differences could be established under the high and low tumorigenicity conditions with regard to DNA adduct formation or persistence. The major difference was the presence of a relatively large extent of pancreatic DNA replication under the high tumorigenic condition. The results indicated that metabolic profile of 4-HAQO, quantity of DNA adducts and levels of DNA replication are key factors involved in initiation of tumorigenesis.     

Characteristics of a Urate-Degrading Diamine Oxidase-Peroxidase Enzyme System in Soybean Radicles

The cadaverine content of soybean radicles showed a maximumpeak 3–4 days after planting. The variation coincidedwith radicle uricase activity during seed germination. The uricase activity could not be fractionate when the bufferpH for the extraction was at 6.0. The addition of 1 M KCl orNaCl to the buffer allowed the extraction of the uricase activity,but an addition of 1 M MgCl₂ or BaCl₂ inhibited this enzyme'sactivity. The urate-degrading enzyme system was purified 248-fold permilligram of protein from soybean radicles. The respective K_mvalues of the diamine oxidase activity for cadaverine and ofthe urate-degrading activity for hydrogen peroxide and uratewere 1.25, 2.93 and 50.3 µM. Analysis by gel electrophoresisof the partially purified enzyme fraction revealed that theurate-degrading enzyme system consisted of a peroxidase thatdegrades urate with hydrogen peroxide and a diamine oxidasethat releases hydrogen peroxide. These data are evidence that a urate-degrading diamine oxidaseand peroxidase system exists in soybean radicles and that thereaction rate of urate-degradation is controlled by the concentrationof cadaverine. (Received November 28, 1984; Accepted April 8, 1985)     

Purification of Ribulose 5-phosphate Kinase and Minor Polypeptides of Pyrenoid from the Green Alga Bryopsis maxima

Ribulose 5-phosphate (Ru5P) kinase (ATP:D-ribulose 5-phosphate1-phosphotrans- ferase; EC 2.7.1.19 [EC] ), an enzyme in the reductivepentose phosphate cycle, was purified from the green alga Bryopsismaxima and its activity and peptide composition were studied.The specific activity of purified Ru5P kinase was 20 µmoleRuBP formed (mg protein)^–1 min^–1 corresponding toa 490-fold purification from the supernatant of chloroplasts.The K_m values of Ru5P kinase for ATP and Ru5P were 69 µMand 330 µM, respectively. The molecular size of Ru5P kinase was estimated as 90 kDa bygel filtration and that of its polypeptide as 41 kDa by SDS-polyacrylamidegel electrophoresis. A small portion of the Ru5P kinase wasfound in a large molecular state (500 kDa) which was consideredto be an inactive form of the enzyme. Ru5P kinase activity has been reported in the pyrenoid of Eremosphaeraviridis as well as ribulose 1,5-bisphosphate carboxylase-oxygenase(RuBisCO) and ribose 5-phosphate isomerase activity (Holdsworth1971). In Bryopsis maxima, among the pyrenoid polypeptides otherthan that of RuBisCO, we found a polypeptide of 42 kDa, similarto that of Ru5P kinase in molecular size and ratio to RuBisCO.A peptide map of the 42 kDa pyrenoid polypeptide, however, showedthat it differed from that of Ru5P kinase. In conclusion, Ru5Pkinase may be not involved in the pyrenoid of this alga. (Received January 19, 1985; Accepted May 15, 1985)     

Inhibition of Photosynthesis by Sulfite in Mesophyll Protoplasts Isolated from Vicia faba L. in Relation to Intracellular Sulfite Accumulation

Inhibition of photosynthesis by Na₂SO₃ in mesophyll protoplastsisolated from Vicia faba leaves and uptake of sulfite by theprotoplasts were examined at various pH values of the incubationmedium containing Na₂SO₃. As the pH of the incubation mediumlowered, the rate of photosynthesis in the protoplasts decreasedand the amount of sulfite taken up by the protoplasts increased.Most of sulfite accumulated in the protoplasts was not metabolizedduring the dark incubation, as measured with an ion chromatograph.Photosynthetic O₂ evolution by the chloroplasts isolated fromVicia mesophyll protoplasts was inhibited by exogenously-appliedNa₂SO₃ over pH region examined (7.4–9.0). The sulfiteconcentration required for a half inhibition of photosynthesisby the isolated chloroplasts was similar to the intracellularsulfite level required for that by the protoplasts. These resultsindicate that the intracellular sulfite accumulated in the protoplastsin an unmetabolized state is responsible for the inhibitionof protoplast photosynthesis. (Received January 24, 1985; Accepted May 29, 1985)     

Phenotype character of the methylglyoxal resistance gene in Saccharomyces cerevisiae: expression in Escherichia coli and application to breeding wild-type yeast strains

The gene responsible for the methylglyoxal resistance of Saccharomyces cerevisiae was cloned, and its phenotypic characteristics were investigated. S. cerevisiae cells with the gene could accumulate large amounts of glutathione in the medium and should remarkably high resistance to various toxic compounds such as methylglyoxal, tetramethylthiuram disulfide, iodoacetamide, and heavy-metal ions. The gene was also expressed in Escherichia coli cells, and the resistance of E. coli cells to toxic compounds also increased as observed for S. cerevisiae cells. The phenotypic characteristics of the gene were applicable to the selection of the transformants of wild-type yeast strains having no genetic markers.     

An investigation for the occurrence of C4 photosynthesis in the Cyperaceae from Australia

Two hundred and twenty species of 38 genera in the Cyperaceae from Australia were examined for the possible occurrence of the C₄ photosynthesis and the anatomical features of leaves and culms. The Kranz type of anatomy and the carbon isotope ratios typical of C₄ plants were found in 84 species in the following six genera of four tribes belonging to subfamily Cyperoideae:Bulbostylis, Crosslandia, andFimbristylis (Fimbristylideae);Lipocarpha (Lipocarpheae);Cyperus (Cypereae);Rhynchospora (Rhynchosporeae). The anatomical observation revealed that the C₄ species possessed any one of the three Kranz anatomical types found by previous investigators. It was suggested that in the Cyperaceae the C₄ syndrome evolved independently within several taxa of the subfamily. The relative distribution of C₃ and C₄ species of the Cyperaceae in Australia was investigated by use of floristic data. It was recognized that the C₄ species dominated in the northern part of the continent which was characterized by tropical and subtropical savannas and hot dry areas with summer rainfall, and the C₃ species in the southern part, which contained temperate areas and mediterranean climatic areas with winter rainfall.     

Differences in Ca2+ mobilization induced by alpha-adrenergic agonist and phosphatidic acid in cultured hepatocytes

In an attempt to elucidate the relationship between phosphatidylinositol breakdown and alpha-adrenergic responses, effects of phosphatidic acid and phosphatidylinositol related metabolites on Ca²⁺ mobilization and glucose output in cultured hepatocytes were examined. Norepinephrine induced the net ⁴⁵Ca²⁺ efflux from preloaded cells and stimulated glucose output via alpha-adrenergic receptor stimulation, whereas phosphatidic acid caused ⁴⁵Ca²⁺ uptake to cells and did not stimulate glucose output. Myo-inositol-monophosphate, diglyceride and arachidonic acid, which are released by phosphatidylinositol breakdown, had no effect on ⁴⁵Ca²⁺ efflux and glucose output in cells. These results suggest that phosphatidic acid and phosphatidylinositol related metabolites can not mimic the alpha-adrenergic actions in cultured hepatocytes.