银杏科研的主要成就和展望

前言银杏又名白果,是现存种子植物中最古老的孑遗植物,也是源于我国的特有珍贵树种。学者们一向把它视为植物界的奇珍,在植物分类学、树木学、果树栽培学和古植物学上占有特殊的位置,至今国内外植物学家、地质学家,以及果树栽培学家们,仍对它进行着深入细致的研究。银杏的科学奥秘将逐步被揭开。     

子宫颈糜烂病毒病因的探讨

491份宫颈拭子病毒分离结果表明:糜烂宫颈单纯疱疹病毒(HSV)分离阳性率(30.8％)是正常宫颈(2.6％)的11.8倍,用人干扰素治疗一个疗程后,病毒分离率下降至疗前的1/4.36例糜烂宫颈活体组织DNA分子杂交表明,乳头瘤病毒16型(HPV-16)阳性者占52.8和,HPV-18占17.9％,HPV-6B占28.1％,HPV-11占7.7％,251例宫颈糜烂患者经人(?)D型基因工程干扰素双盲对比治疗后,总有效率达93.8％,显效率达60％,分析临床疗效与HSV分离率的变化表明,临床有效病例中有35％(49/140)在治疗后病毒阴转,有57％在疗前疗后均未分离出HSV,有5％在疗前疗后保持阳性不变,有2.9％疗前阴性,疗后阳性,上述结果表明,HSV和HPV与慢性宫颈炎有一定关系。     

Electrophoretic behavior of the H+-ATPase proteolipid from bovine heart mitochondria

The proteolipid subunit of H⁺-ATPase was labeled by [¹⁴C]N,N-dicyclohexylcarbodiimide in bovine heart mitochondria. The radioactive labeling was followed using various systems of sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE). When using discontinuous SDS-PAGE (Laemmli, U.K., 1970,Nature (London)227, 680–685) a monomeric (Mr 7600±1500) and a dimeric form (Mr 17,800±1200) of the proteolipid were detected, while only the monomeric form was found on urea (8 M) containing gels (SDS-PAGE according to Laemmli; or Swank, R. T., and Munkers, K. D., 1971,Anal. Biochem. 39, 462–477). When using SDS-PAGE with Na-P_i buffer (Weber, K., and Osborn, M., 1969,J. Biol. Chem. 244, 4406–4442), only a dimeric form of the proteolipid (Mr 15,000±1000) was detected. Experimental data indicate that the different patterns of proteolipid separation are related to the presence of the two distinct proteolipid conformations in the SDS solution.     

Microbial oxidation of methanol: Purification and properties of formaldehyde dehydrogenase from a Pichia sp. NRRL-Y-11328

An NAD⁺-linked, reduced glutathione-dependent formaldehyde dehydrogenase was purified to homogeneity from soluble extracts of methanol-grown yeast, Pichia sp. Formaldehyde and methylglyoxal are oxidized in the presence of NAD⁺ as an electron acceptor. NADP⁺ could not replace NAD⁺. Other straight chain aldehydes (C₂–C₆ tested), branched-chain aldehydes (e.g., isobutyaldehyde), aromatic aldehydes (e.g., salicylal-dehyde, benzaldehyde), glutyraldehyde, glyceraldehyde, glycoaldehyde, and glyoxal-dehyde tested were not oxidized by the purified formaldehyde dehydrogenase. The product of formaldehyde oxidation by purified enzyme was demonstrated to be S-for-mylglutathione by measuring the absorption at 240 nm due to the formation of thioester of formaldehyde and reduced glutathione. The K_m values for NAD⁺, formaldehyde, and reduced glutathione were 0.12, 0.31, and 0.16 mm, respectively, for the forward reaction at pH 8.0. The purified formaldehyde dehydrogenase also catalyzed the reduction of S-formylglutathione in the presence of NADH. Formate was not reduced by the purified enzyme. The K_m values for S-formylglutathione and NADH were 0.60 and 0.25 mm, respectively, for the reverse reaction at pH 6.0. Formaldehyde dehydrogenase has a molecular weight of 84,000 as determined by gel filtration and subunit molecular weight of 41,000 as determined by sodium dodecyl sulfate-gel electrophoresis. S-Formylglutathione, a product of formaldehyde oxidation, was oxidized by the partially purified formate dehydrogenase from Pichia sp. Formate dehydrogenase has a higher affinity toward S-formylglutathione (K_m value 1.8 mm) than toward formate (K_m value 25 mm). Antiserum prepared against the purified formaldehyde dehydrogenase from Pichia sp. NRRL-Y-11328 forms strong precipitin bands with isofunctional enzymes from methanol-grown Pichia pastoris NRRL-Y-7556 and Torulopsis candida Y-11419 and weak precipitin bands with Hansenula polymorpha NRRL-Y-2214. No cross-reaction was observed with isofunctional enzyme derived from methanol-grown Kloeckera sp.     

Epoxidation of Short-Chain Alkenes by Resting-Cell Suspensions of Propane-Grown Bacteria

Sixteen new cultures of propane-utilizing bacteria were isolated from lake water from Warinanco Park, Linden, N.J. and from lake and soil samples from Bayway Refinery, Linden, N.J. In addition, 19 known cultures obtained from culture collections were also found to be able to grow on propane as the sole carbon and energy source. In addition to their ability to oxidize n-alkanes, resting-cell suspensions of both new cultures and known cultures grown on propane oxidize short-chain alkenes to their corresponding 1,2-epoxides. Among the substrate alkenes, propylene was oxidized at the highest rate. In contrast to the case with methylotrophic bacteria, the product epoxides are further metabolized. Propane and other gaseous n-alkanes inhibit the epoxidation of propylene. The optimum conditions for in vivo epoxidation are described. Results from inhibition studies indicate that a propane monooxygenase system catalyzes both the epoxidation and hydroxylation reactions. Experiments with cell-free extracts show that both hydroxylation and epoxidation activities are located in the soluble fraction obtained after 80,000 × g centrifugation.     

Production of Methyl Ketones from Secondary Alcohols by Cell Suspensions of C2 to C4n-Alkane-Grown Bacteria

Nineteen new C₂ to C₄n-alkane-grown cultures were isolated from lake water from Warinanco Park, Linden, N.J., and from lake and soil samples from Bayway Refinery, Linden, N.J. Fifteen known liquid alkane-utilizing cultures were also found to be able to grow on C₂ to C₄n-alkanes. Cell suspensions of these C₂ to C₄n-alkane-grown bacteria oxidized 2-alcohols (2-propanol, 2-butanol, 2-pentanol, and 2-hexanol) to their corresponding methyl ketones. The product methyl ketones accumulated extracellularly. Cells grown on 1-propanol or 2-propanol oxidized both primary and secondary alcohols. In addition, the activity for production of methyl ketones from secondary alcohols was found in cells grown on either alkanes, alcohols, or alkylamines, indicating that the enzyme(s) responsible for this reaction is constitutive. The optimum conditions for in vivo methyl ketone formation from secondary alcohols were compared among selected strains: Brevibacterium sp. strain CRL56, Nocardia paraffinica ATCC 21198, and Pseudomonas fluorescens NRRL B-1244. The rates for the oxidation of secondary alcohols were linear for the first 3 h of incubation. Among secondary alcohols, 2-propanol and 2-butanol were oxidized at the highest rate. A pH around 8.0 to 9.0 was found to be the optimum for acetone or 2-butanone formation from 2-alcohols. The temperature optimum for the production of acetone or 2-butanone from 2-propanol or 2-butanol was rather high at 60°C, indicating that the enzyme involved in the reaction is relatively thermally stable. Metal-chelating agents inhibit the production of methyl ketones, suggesting the involvement of a metal(s) in the oxidation of secondary alcohols. Secondary alcohol dehydrogenase activity was found in the cell-free soluble fraction; this activity requires a cofactor, specifically NAD. Propane monooxygenase activity was also found in the cell-free soluble fraction. It is a nonspecific enzyme catalyzing both terminal and subterminal oxidation of n-alkanes.     

Preferential degradation of the terminal carbohydrate moiety of membrane glycoproteins in rat hepatoma cells and after transfer to the membranes of mouse fibroblasts

Glycoproteins in the plasma membrane of rat hepatoma cells were labeled at their externally exposed tyrosine residues with 131I and at their galactose and sialic acid residues with 3H. The degradation of both isotopes in the total cell protein fraction, in glycoproteins purified by concanavalin A, and in glycoproteins separated on two-dimensional gels was determined. Similarly, the total cellular membrane glycoproteins were metabolically labeled with [35S]methionine and [3H]fucose. The fate of both incorporated labels was followed by lectin chromatography or by precipitation of the proteins with specific antibodies followed by electrophoretic gel separation. In both labeling experiments, the carbohydrate markers were lost from the ligand- recognized fraction with similar kinetics as from the total cell protein fraction. In some glycoprotein species which were separated by two-dimensional gel electrophoresis, the polypeptide portion exhibited up to a twofold slower rate of degradation relative to that of the carbohydrate moiety. This difference is most pronounced in carbohydrate- rich glycoproteins. To corroborate this finding, double-labeled membrane glycoproteins were incorporated into reconstituted phospholipid vesicles which were then transferred via fusion into the plasma membrane of mouse fibroblasts. Both the polypeptide and carbohydrate moieties of the transferred membrane glycoproteins were degraded with the same relative kinetics as in the original hepatoma cells. The rate of degradation is mostly a function of the structural properties of the membrane components as shown by the preservation of metabolically stable fucogangliosides of Reuber H-35 hepatoma cells transferred onto the fibroblasts. The technique of insertion of membrane components into the plasma membrane of another cell should assist in the elucidation of the exact route and mechanism of membrane protein destruction.     

Substrate Specificity of Actinoplanes Antibiotic Peptide Lactonases

A constitutive peptide lactonase from Actinoplanes missouriensis hydrolyzed echinomycin, stendomycin, thiostrepton, vernamycin B, staphylomycin S, and etamycin. An induced lactonase hydrolyzed actinomycin but not the other peptide lactones.