The isolation and properties of phenylalanine hydroxylase from human liver

Phenylalanine hydroxylase was prepared from human foetal liver and purified 800-fold; it appeared to be essentially pure. The phenylalanine hydroxylase activity of the liver was confined to a single protein of mol.wt. approx. 108000, but omission of a preliminary filtration step resulted in partial conversion into a second enzymically active protein of mol.wt. approx. 250000. Human adult and full-term infant liver also contained a single phenylalanine hydroxylase with molecular weights and kinetic parameters the same as those of the foetal enzyme; foetal, newborn and adult phenylalanine hydroxylase are probably identical. The K(m) values for phenylalanine and cofactor were respectively one-quarter and twice those found for rat liver phenylalanine hydroxylase. As with the rat enzyme, human phenylalanine hydroxylase acted also on p-fluorophenylalanine, which was inhibitory at high concentrations, and p-chlorophenylalanine acted as an inhibitor competing with phenylalanine. Iron-chelating and copper-chelating agents inhibited human phenylalanine hydroxylase. Thiol-binding reagents inhibited the enzyme but, as with the rat enzyme, phenylalanine both stabilized the human enzyme and offered some protection against these inhibitors. It is hoped that isolation of the normal enzyme will further the study of phenylketonuria.     

Identification and genetic control of starch-degrading enzymes in maize endosperm

Three starch-degrading enzymes from liquid endosperm of maize have been separated by means of horizontal acrylamide gel electrophoresis. The three enzymes are tentatively identified as -amylase (zone 1), -amylase (zone 2), and -glucan phosphorylase (zone 3). Electrophoretic variants of these enzymes were found among ten inbred strains examined. Results of genetic crosses with respect to zone 2 amylase show that it is controlled by a pair of alleles (Amy-2 ^A and Amy-2 ^B) acting without dominance. It further appears that Amy-2 and Ct (catalase) are linked with 5% recombination frequency.This work was supported by the U.S. Atomic Energy Commission, under contract No. AT(11-1)-1338.     

Carbon Balance of a Mannitol Fermentation and the Biosynthetic Pathway

The carbon balance was determined for a fermentation in which mannitol is produced from glucose by an Aspergillus species. The products found were: cells (17% of carbon input), CO(2) (26%), mannitol (35%), glycerol (10%), erythritol (2.5%), glycogen (1%), and unidentified compounds (8%). Thus, 92% of the carbon input was accounted for. Cell-free enzyme studies showed that mannitol was synthesized via the reduction of fructose-6-phosphate and not by the direct reduction of fructose. If the cell yield from glucose was assumed to be 50% and the theoretical conversion efficiency from glucose to polyols was 90%, as calculated from the energy balance, then 34% of the glucose carbon was used for growth and 53% was used for polyol formation.     

三乙醇胺基强碱性聚苯乙烯树脂共价固定胰酶的研究

用多孔强碱型三乙醇胺基聚苯乙烯阴离子交换树脂做为载体,用CNBr与载体上的多羟基作用共价偶联了胰酶。红外光谱表明:其共价偶联反应机理与用CNBr活化多糖类载体并接酶的机理相类似。最适偶联条件研究表明:CNBr用量增多,酶蛋白载量增加。但比活下降。偶联pH为10时,固定化酶有适宜的载量和较高的比活。由于胰酶水解蛋白反应释放出H~+质子,这些质子在载体内积累,使微环境内H~+质子浓度增加,进而使得固定化胰酶的pH—活性曲线在pH9～11范围内未出现下降。在变温和60℃恒温下对固定化酶的热稳定性测试表明:固相酶的热稳定性比天然酶的热稳定性有所提高。     

贵州省赤水县桫椤调查初报

国家一级重点保护植物桫椤,目前世界上少数国家尚存,国内除华南、西南地区及台湾等少数省份外亦不多见。其中贵州省赤水县桫椤不仅面积广,且数量多,生长旺。据不完全统计,全县35个乡中,有20个乡有分布,面积     

Molecular diversity of L-type calcium channels. Evidence for alternative splicing of the transcripts of three non-allelic genes

The diversity of L-type calcium channels was probed using the polymerase chain reaction and primers based on regions conserved in the L-type skeletal muscle (CaCh 1) and cardiac calcium channels (CaCh 2). Related sequences were amplified from human heart, hamster heart, rabbit heart, mouse ovary, mouse BC3H1 cells, and hamster insulin-secreting (HIT) cells. Sequencing of various clones revealed the presence of alternate splicing in gene products coding for CaCh 1, CaCh 2, and a related calcium channel. This related gene product, which we refer to as neuroendocrine or CaCh 3, is expressed in brain and endocrine cells. The diverse products can be explained by the use of alternate exons of equal size, which account for changes in amino acid composition, in combination with an alternate splice acceptor site or an exon skipping event, which produces channels of variable length. Four variants were defined for the gene 3 product, subtypes 3a, 3b, 3c, and 3d that differed in both the sequence of the third membrane spanning segment of the fourth repeat unit (IVS3) and in the size of the linker between this and the fourth membrane spanning segment (IVS4). Three CaCh 2 variants were cloned, subtypes 2a, 2c, and 2d, that are homologous to the a, c, and d variants of CaCh 3. For the skeletal muscle calcium channel only two variants were isolated. They are homologous to those of the a and c subtypes of CaCh 2 or 3, in that they differ only in the size of the IVS3 to IVS4 linker. These results demonstrate that calcium channel diversity is created by both the expression of distinct genes and the alternate splicing of these genes.     

Structure and assembly of turnip crinkle virus. VI. Identification of coat protein binding sites on the RNA

Structural studies of turnip crinkle virus have been extended to include the identification of high-affinity coat protein binding sites on the RNA genome. Virus was dissociated at elevated pH and ionic strength, and a ribonucleoprotein complex (rp-complex) was isolated by chromatography on Sephacryl S-200. Genomic RNA fragments in the rp-complex, resistant to RNase A and RNase T1 digestion and associated with tightly bound coat protein subunits, were isolated using coat-protein-specific antibodies. The identity of the protected fragments was determined by direct RNA sequencing. These approaches allowed us to study the specific RNA-protein interactions in the rp-complex obtained from dissociated virus particles. The location of one protected fragment downstream from the amber terminator codon in the first and largest of the three viral open reading frames suggests that the coat protein may play a role in the regulation of the expression of the polymerase gene. We have also identified an additional cluster of T1-protected fragments in the region of the coat protein gene that may represent further high-affinity sites involved in assembly recognition.     

大肠杆菌棉子糖操纵子α—半乳糖苷酶表达的调节控制

The alpha-galactosidase, coded for by the first structural gene rafA in the plasmid determined raf operon was an inducible enzyme. In contrast to lac or mel operon, raf operon has more strict structural specificity for inducers. The enzyme can be induced by melibiose and raffinose, or weakly by D-galactose, but not by structurally related sugars such as lactose, PNPG etc.. The alpha-galactosidase forming capacity as function of growth curve reached a single peak at the end of the logarithmic phase of the growth. The structure and regulation of raf operon is similar to those of lac operon. The repressormor-mediated negative control plays a major role in the regulation of raf operon, and cAMP-CAP mediated positive control is also involved in the regulation. When 0.4% glucose was added into the medium with other carbon sources, the expression of the enzyme was repressed by 2-3 fold. Transient catabolite repression has been observed neither in inducible nor constitutive alpha-galactosidase expression. Based on alpha-galactosidase assay, in mutant strains CA8306(cya) and CA8445 (cya, crp) the expression level of raf operon was only 9% and 2.5% of that in wild type strain respectively. The glucose effect or the repression in cya mutant can be abolished by 1-5 mmol cAMP. The constitutive alpha-galactosidase expression in cya and cry double mutant (CA8445) remains repressible by glucose, but irreversible by cAMP, suggesting cAMP-CAP complex is not the exclusive mediator of the catablite repression.(ABSTRACT TRUNCATED AT 250 WORDS)     

小蜉属小蜉亚属一新种：蜉蝣目：小蜉科

本文记述小蜉属小蜉亚属 subgenus Ephemerella Walsh 一新种,小蜉亚属种类多,全世界已知有40种左右,广布于北美、苏联、日本等国,但中国尚未发现,因此本文也是小蜉亚属在中国的首次报道。