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81.
Chronic hyperphenylalaninemia maintained with the aid of a suppressor of phenylalamine hydroxylase, -methylphenylalanine, increases the glycine concentration and the phosphoserine phosphatase activity of the developing rat brain but not that of liver or kidney. Similar increases occur after daily injections with large doses of phenylalanine alone, while tyrosine, isoleucine, alanine, proline, and threonine, were without effect. Treatment with methionine, which increases the phosphoserine phosphatase activity of the brain and lowered that of liver and kidney, left the cerebral glycine level unchanged. When varying the degrees of gestational or early postnatal hyperphenylalaninemia, a significant linear correlation was found between the developing brains' phosphoserine phosphatase and glycine concentration. Observations on the uptake of injected glycine and its decline further indicate that coordinated rises in the brain's phosphoserine phosphatase and glycine content associated with experimental hyperphenylalaninemia denote a direct impact of phenylalanine on the intracellular pathway of glycine synthesis in immature animals. 相似文献
82.
Luc Giasson Charles A. Specht Craig Milgrim Charles P. Novotny Robert C. Ullrich 《Molecular & general genetics : MGG》1989,218(1):72-77
Summary An A mating-type allele (A4) was isolated by walking the chromosome from the closely linked PAB1 gene. A cosmid clone containing the A1 allele isolated from the walk was used as a probe to recover the A1 allele from another cosmid library. Cosmids encoding mating-type activity were identified by transforming Schizophyllum cells and screening for activation of A-regulated development. Putative mating-type transformants were confirmed in mating tests and genetic analyses of progeny. The identity of the specific alleles isolated was demonstrated by showing that their effectiveness in transforming for mating type is limited to recipient strains possessing an A allele different from the one encoded by the cloned sequences. Transforming DNA is active in trans, suggesting that A encodes a diffusible product. Restriction mapping shows that A1 and A4 are coded in the same physical region of the genome, but within a subregion that contains extensive sequence divergence. In addition, Southern analyses show that there is only one copy of A1 or A4 per haploid genome, and that they do not cross-hybridize to one another or to any of the other A alleles. A1 and A4 were subcloned as 2.8 and 1.2 kb fragments, respectively, retaining in transformation all the mating-type activity demonstrated of the original cosmids. 相似文献
83.
84.
Philippe Lejeune Philippe Bertin Corinne Walon Karine Willemot Charles Colson Antoine Danchin 《Molecular & general genetics : MGG》1989,218(2):361-363
Summary Spontaneous mutants of Escherichia coli K12 displaying an increased level of the kanamycin resistance conferred by plasmid pGR71 were selected. Several mutants obtained in this way apparently carry large chromosomal deletions extending into galU and/or bglY (27 min). This positive selection of deletions allowed detection of a new locus located between galU and bglY. Deletions of this locus are responsible for increased resistance to kanamycin (Irk), decreased resistance to l-serine in minimal medium (Drs) and decreased resistance to chloramphenicol (Drc) when a cat gene is present in the bacteria. 相似文献
85.
Komandoor E. Achyuthan Ann Mary Robin Bhaermani Charles S. Greenberg 《Molecular and cellular biochemistry》1989,85(1):57-65
Calcium ions are crucial for expression of transglutaminase activity. Although lanthanides have been reported to substitute for calcium in a variety of protein functions, they did not replace the calcium requirement during transglutaminase activity measurements. Furthermore, lanthanides strongly inhibited purified liver transglutaminase activity using either casein or fibrinogen as substrates. Terbium (III) inhibition of transglutaminase-catalyzed putrescine incorporation into casein was not reversed by the presence of 10–200 fold molar excess of calcium ions (Ki for Tb(III)=60 µM). Conformational changes in purified liver transglutaminase upon Tb(III) binding were evident from a biphasic effect of Tb(III) on transglutaminase binding to fibrin. Low concentrations of Tb(III) (1 µM to 10 µM inhibited the binding of transglutaminase to fibrin, whereas higher concentrations (20 µM to 100 µM promoted binding. Conformational changes in purified liver transglutaminase consequent to Tb(III) binding were also demonstrated by fluorescence spectroscopy due to Forster energy transfer. Fluorescence emission was stable to the presence of 200 mM NaCl and 100 mM CaCl2 only partially quenched emission. Purified liver transglutaminase strongly bound to Tb(III)-Chelating Sepharose beads and binding could not be disrupted by 100 mM CaCl2 solution. Our data suggest that Tb(III)-induced conformational changes in transglutaminase are responsible for the observed effects on enzyme structure and function. The potential applications of Tb(III)-transglutaminase interactions in elucidating the structure-function relationships of liver transglutaminase are discussed. 相似文献
86.
Aflatoxin contamination of agricultural commodities continues to be a serious problem in the United States. Breeding for resistant genotypes has been unsuccessful and detoxification of food sources is not economically feasible. New strategies for control may become apparent once more is known about the biosynthesis and regulation of aflatoxin. Although the biosynthetic pathway of aflatoxin has been extensively studied, little is known about the regulation of the individual steps in the pathway. We have developed a genetic transformation system forAspergillus flavus that provides a new and expedient approach to studying the biosynthesis of aflatoxin and its regulation. Through the use of this genetic transformation system, genes for aflatoxin biosynthesis can be identified and isolated by the complementation of aflatoxin negative mutants. In this paper we discuss molecular strategies for studying the regulation and biosynthesis of aflatoxin. 相似文献
87.
Curtis W. Hoganson Demetrios F. Ghanotakis Gerald T. Babcock Charles F. Yocum 《Photosynthesis research》1989,22(3):285-293
Manganese in the oxygen-evolving complex is a physiological electron donor to Photosystem II. PS II depleted of manganese may oxidize exogenous reductants including benzidine and Mn2+. Using flash photolysis with electron spin resonance detection, we examined the room-temperature reaction kinetics of these reductants with Yz
+, the tyrosine radical formed in PS II membranes under illumination. Kinetics were measured with membranes that did or did not contain the 33 kDa extrinsic polypeptide of PS II, whose presence had no effect on the reaction kinetics with either reductant. The rate of Yz
+ reduction by benzidine was a linear function of benzidine concentration. The rate of Yz
+ reduction by Mn2+ at pH 6 increased linearly at low Mn2+ concentrations and reached a maximum at the Mn2+ concentrations equal to several times the reaction center concentration. The rate was inhibited by K+, Ca2+ and Mg2+. These data are described by a model in which negative charge on the membrane causes a local increase in the cation concentration. The rate of Yz
+ reduction at pH 7.5 was biphasic with a fast 400 s phase that suggests binding of Mn2+ near Yz
+ at a site that may be one of the native manganese binding sites.Abbreviations PS II
Photosystem II
- YD
tyrosine residue in Photosystem II that gives rise to the stable Signal II EPR spectrum
- Yz
tyrosine residue in Photosystem II that mediates electron transfer between the reaction center chlorophyll and the site of water oxidation
- ESR
electron spin resonance
- DPC
diphenylcarbazide
- DCIP
dichlorophenolindophenol 相似文献
88.
Flavio Massimo Garlaschi Giuseppe Zucchelli Robert Charles Jennings 《Photosynthesis research》1989,20(3):207-220
An experimental analysis is presented concerning the effect on relative light absorption by the two photosystems caused by (a) a highly light scattering environment (the detour effect) and (b) light filtration across successive chloroplast layers (the light attenuation effect). Both suspensions of isolated chloroplasts and leaves were employed.It is concluded that within a single spinach leaf these phenomena are likely to lead to only rather small increases in relative photosystem I absorption and activity with respect to photosystem II and will thus not exert a significant effect on non cyclic electron transport. On the contrary when light is filtrated across successive vegetation layers (shade light) significant increases in the relative PSI absorption and activity may be encountered.It is determined that the detour effect in mature leaves from a variety of plants increases overall photosynthetically useful light absorption by 35–40%.Abbreviations FM
maximal fluorescence
- LHCP2
light-harvesting chlorophyl a/b protein complex II
- QA-primary
quinone acceptor of photosystem II 相似文献
89.
90.
Higher order structure is present in the yeast nucleus: autoantibody probes demonstrate that the nucleolus lies opposite the spindle pole body 总被引:5,自引:0,他引:5
A panel of sera from 892 autoimmune patients was screened by indirect immunofluorescence on mammalian cells. Seventy-three sera were identified that recognize the nucleolus. Three of these sera appear to stain the nucleolus in yeast, suggesting that they recognize highly conserved antigens. These three sera also immunoprecipitate mammalian U3 snRNA-containing particles, which reside in the nucleolus and have been implicated in rRNA processing. Double immunofluorescence experiments with anti-nucleolus and anti-tubulin antibodies revealed a novel form of non-random nuclear organization in yeast. The spindle pole body and the nucleolus — both of which are associated with the nuclear envelope — preferentially localize at opposite ends of the nucleus. Organization of these and other components into specific regions of the nucleus may be important for optimizing their proper function. 相似文献