Immobilization of pig muscle 3-phosphoglycerate kinase

3-Phosphoglycerate kinase (ATP:3-phospho-d-glycerate 1-phosphotransferase, EC 2.7.2.3) has been covalently immobilized on a polyacrylamide-type support containing carboxylic groups activated by water-soluble carbodiimide. The activity was 88 units g^?1 xerogel. The activity versus pH profile showed a sharper maximum at pH 6.5 in the case of the immobilized enzyme. The immobilized enzyme had a broad apparent optimum temperature range between 40 and 50°C. The apparent K_m values of the immobilized 3-phosphoglycerate kinase were lower for both 3-phosphoglycerate and ATP than those of the soluble enzyme. In the case of the immobilized enzyme stabilities were enhanced.     

Electrical effects of potassium and bicarbonate on proximal tubule cells ofNecturus

Summary The effects of stepwise concentration changes of K⁺ and HCO ₃ ^– in the basolateral solution on the basolateral membrane potential (V _bl) of proximal tubule cells of the doubly-perfusedNecturus kidney were examined using conventional microelectrodes. Apparent transference numbers were calculated from changes inV _bl after alterations in external K⁺ concentration from 1.0 to 2.5mm (t _{K, 1.0–2.5}), 2.5 to 10, and in external HCO ₃ ^– concentration (at constant pH) from 5 to 10mm (t _{HCO3, 5–10}), 10 to 20, or 10 to 50.t _{K, 2.5–10} was 0.38±0.02 under control conditions but was sharply reduced to 0.08±0.03 (P>0.001) by 4mm Ba⁺⁺. This concentration of Ba⁺⁺ reducedV _bl by 9±1 mV (at 2.5 external K⁺). Perfusion with SITS (5×10^–4 m) for 1 hr hyperpolarizedV _bl by 10±3 mV and increasedt _{K, 2.5–10} significantly to 0.52±0.01 (P<0.001). Ba⁺⁺ application in the presence of SITS depolarizedV _bl by 22±3 mV. In control conditionst _{HCO3, 10–50} was 0.63±0.05 and was increased to 0.89±0.07 (P<0.01) by Ba⁺⁺ but was decreased to 0.14±0.02 (P<0.001) by SITS. In the absence of apical and basolateral chloride, the response ofV _bl to bicarbonate was diminished but still present (t _{HCO3, 10–20} was 0.35±0.03). Intracellular pH, measured with liquid ion-exchange microelectrodes, increased from 7.42±0.19 to 7.57±0.17 (P<0.02) when basolateral bicarbonate was increased from 10 to 20mm at constant pH. These data show that the effects of bicarbonate onV _bl are largely independent of effects on the K⁺ conductance and that there is a significant current-carrying bicarbonate pathway in the basolateral membrane. Hence, both K⁺ and HCO ₃ ^– gradients are important in the generation ofV _bl, and their relative effects vary reciprocally.     

β-decay,Bremsstrahlen, and the origin of molecular chirality

Summary A brief review is presented of the Vester-Ulbricht -decay Bremsstrahlen hypothesis for the origin of optical activity, and of subsequent experiments designed to test it. Certain of our experiments along these lines, begun in 1974 and involving the irradiation of racemic and optically active amino acids in a 61.7 KCi⁹⁰Sr–⁹⁰Y Bremsstrahlen source, have now been completed and are described. After 10.89 years of irradiation with a total Bremsstrahlen dose of 2.5×10⁹ rads, crystallinedl-leucine, norleucine, and norvaline suffered 47.2, 33.6, and 27.4% radiolysis, respectively, but showed no evidence whatsoever of asymmetric degradation.d- andl-Leucine underwent about 48% radiolysis and showed 2.4–2.9% radioracemization. Other samples in solution were too severely degraded to analyze. Probable intrinsic reasons for the failure of the Vester-Ulbricht mechanism to afford asymmetric radiolysis in the present and related experiments involving -decay Bremsstrahlen are enumerated.A portion of this material was presented at the 7th International Conference on the Origins of Life, Mainz, FRG, July 10–15, 1983     

海枣曲霉β-半乳糖苷酶的提纯与性质

 通过过聚乙二醇6000-磷酸钾缓冲液双相分离、Sephadex G-100凝胶过滤、DEAE-Sephadex A-50离子交换层析、羟基磷灰石层析及SephadexG-100凝胶过滤等提纯步骤,从海枣曲霉(Aspergillus phoenicis)麦麸培养物抽提液中提纯得到凝胶电泳均一的β-半乳糖苷酶。该酶的最适pH为3.5—4.0,最适温度为60℃(反应15分钟),在pH5.0—8.5之间及60℃以下稳定。在65℃和70℃保温时失活50％的时间分别为27和2分钟。用SDS凝胶电泳法和梯度凝胶电泳法分别测得该酶的分子量为115,000和118,000。薄层凝胶等电聚焦法测得其等电点为pH4.6。     

Hypoxanthine-guanine phosphoribosyltransferase in human erythroid cells: Properties of the isozymes

We have previously given evidence that the hypoxanthine-guanine phosphoribosyltransferase (HGPRT; EC 2.4.2.8) isozymes in human erythroid cells result from posttranslational modifications of a single gene product [Johnson, G. G., et al. (1982). Biochemistry 21:960]. In the present work we compare the properties of the unmodified and two major modified isozymes, which collectively account for 90% of the HGPRT enzyme activity in cell lysates. The modified isozymes differ from the parent molecule in the pH dependence of activity and in the relative utilization of the two purine base substrates, hypoxanthine and guanine. In contrast to the changes in the catalytic properties of the enzyme, the modifications have no detectable effects on the heat stability or on the equilibrium between enzyme dimers and enzyme tetramers.This work was supported by United States Public Health Service Grant 5 RO1 CA 16754-03 and by the San Diego State University Foundation.     

Biochemical and physiological studies of certain ticks (Ixodoidea): specific gravity of hemolymph and coxal and gut fluids of Argas (Persicargas) persicus and Argas (Persicargas) arboreus (Argasidae)

Specific gravity (sp. gr.) of cell-free hemolymph and gut and coxal fluids was determined at different states of the gonotrophic cycle (unfed + 15 days, engorgement day before and after coxal fluid emission, engorgement + 1 day, oviposition day, and oviposition completion + 1 day) of female Argas (Persicargas) persicus and A. (P.) aboreus (Argasidae). The patterns of hemolymph and gut fluid sp. gr. change differed from each other during the gonotrophic cycle, but both patterns were similar in the 2 Argas species. Hemolymph sp. gr. decreased to a minimum one day after feeding (1.0085 and 1.0081 for persicus and arboreus, respectively), and increased through oviposition to a maximum on oviposition + 1 day (1.0187 and 1.0221). Minimum gut fluid sp. gr. occurred on engorgement day before coxal fluid emission (1.0565 and 1.0697). Afterward, gut fluid sp. gr. increased to a maximum on engorgement day + 1 for persicus (1.1089) and on oviposition day for arboreus (1.0973), and then decreased during oviposition in both species. In each tested state of each species, the sp. gr. was consistently higher in gut fluid than in hemolymph. In each species, coxal fluid and hemolymph sp. gr. were the same on engorgement day.     

Analysis of three-dimensional cell imaging obtained with optical microscopy techniques based on defocusing

The properties of an optical microscope are analyzed and analytically evaluated with a simple and effective model in order to understand the true meaning, limitations, and real capabilities of a defocusing technique. Major emphasis is given to the applications related to microscopic objects of biological interest using fluorescence and absorption light microscopy. A procedure for three-dimensional viewing is analyzed and discussed.     

Growth, dry weight partitioning and wood properties of Pinus radiata D. Don after 2 years of CO2 enrichment

Abstract Advanced selections (families 20010 and 20062) of P. radiata D. Don were exposed to either 340 or 660 μmol CO₂ mol ¹ for 2 years to establish if growth responses to high CO₂ would persist during the development of woody tissues. The experiment was carried out in glasshouses and some of the trees at each CO₂ concentration were subjected to phosphorus deficiency and to periodic drought. CO₂ enrichment increased whole-plant dry matter production irrespective of water availability, but only when phosphorus supply was adequate. The greatest increase occurred during the exponential period of growth and appeared to be tied to increased rates of photosynthesis, which caused accelerated production of leaf area. The increase in whole-plant dry matter production was similar for both families; however, family 20010 partitioned larger amounts of dry weight to the trunks than family 20062. which favoured the roots and branches. Wood density was generally increased by elevated CO₂ and for family 20010 this increase was due to thickening of the tracheid walls. Tracheid length was similar at both CO₂ levels but differed between families. These results suggest that, as the atmospheric CO₂ concentration rises, field-grown P. radiata should produce more dry weight at sites where phosphorus is not acutely deficient, even where drought limits growth; however, increases in wood production are likely only for genotypes which continue to partition at least the same proportion of dry weight to wood in the trunk.