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.     

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)     

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.     

Cloning and sequence analysis of cDNA encoding active phosphoenolpyruvate carboxylase of the C4-pathway from maize.

A recombinant clone, pM52, containing cDNA for maize phosphoenolpyruvate carboxylase (PEPCase, EC 4.1.1.31) was isolated from a maize leaf cDNA library constructed using an expression vector in Escherichia coli. The screening of the clone was conveniently performed through its ability to complement the phenotype (glutamate requirement) of PEPCase-negative mutant of E. coli. The enzyme encoded by this clone was identical with the major PEPCase in maize, a key enzyme in the C4-pathway, as judged from its allosteric properties and immunological reactivity. The cloned cDNA (3093 nucleotides in length) contained an open reading frame of 2805 nucleotides, the 3'-untranslated region of 222 nucleotides and the poly(dA) tract of 64 nucleotides. The deduced amino acid sequence (935 residues) of the enzyme showed higher homology with that of an enterobacterium, E. coli (43%) than that of a cyanobacterium (blue-green alga), Anacystis nidulans (33%).     

Staining air dried protoplasts for study of plant chromosomes

The air drying technique used in mammalian cytology was applied to isolated plant protoplasts for study of chromosomes. For cultured celery cells, this technique resulted in good spreads of metaphase chromosomes with high resolution. Mitotic chromosomes of Brassica species are relatively small, poor stained by common stains, and difficult to spread by the squash technique. In this study, however, the chromosomes of B. carinata in callus culture were spread well and stained clearly with Giemsa staining solution. The chromosome preparations by the present techniques should also be amenable to chromosome banding studies in plants.     

Quantitative Analysis of the Inactivation of Photosynthetic Oxygen Evolution and the Release of Polypeptides and Manganese in the Photosystem II Particles of Spinach Chloroplasts

Photosynthetic oxygen evolution by photosystem II particleswas inactivated by treatment with NaCl, NH₂OH or high pH. Whenthe degree of inactivation was compared with the degree of releasefrom the particles of Mn and three polypeptides having molecularmasses of 33, 24 and 18kdaltons, two types of inactivation werefound: one, brought about with 960 mM NaCl, was related to therelease of the 24 kdalton polypeptide, and the other, broughtabout with 1.5 mM NH₂OH or high pH, seemed to be related tothe release of Mn. ¹Present address: Department of Chemistry, Faculty of Science,Toho University, Miyama 2-2-1, Funabashi 274, Japan. (Received January 31, 1983; Accepted March 28, 1983)     

Role of microstructure of nerve impulse train in relation to transmission of neuronal activity and coding mechanism of neural information

Input-output relation were of giant neurons of a marine mollusc, Onchidium verruculatum, and a computer-simulated neuron investigated in terms of microstructure of nerve impulse train. The microstructure of input impulse train, the size of a unitary EPSP, and the extent of spontaneous firing activity of a single neuron had an important influence upon the effective summation of arriving synaptic inputs, the elicitation of output spikes, and intervals between succeeding output spikes. The neuron responded differently to respective input trains with different time structures, i.e. it discriminated input time pattern to various degrees. The manner in discrimination of input time pattern was dependent on the size of the unitary EPSP and the extent of the spontaneous firing activity, if it had. Some discussions were made with regard to possible coding systems of neural signal, assuming a frequency code and/or a pattern code.