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101.
The paper describes the logic of a computer method for identifying unbranched enzyme kinetic mechanisms on the basis of observed initial velocity and product inhibition patterns (Cleland, 1963). The method establishes initially an acceptable order of reactant addition and release, proceeds to list all the mechanisms consistent with that order and the data, and finally determines which of these can also explain data which require either non-competitive or dead-end inhibition. 相似文献
102.
Jeanette J. Chen Erla R. Smith Gary D. Gray Julian M. Davidson 《Primates; journal of primatology》1981,22(2):253-260
Seasonal changes in body weight, plasma testosterone and ejaculatory capacity were observed in five intact and two testosterone-implanted
castrated squirrel monkeys for a total of 13 months. Electroejaculation was employed for obtaining data concerning ejaculation.
In the intact animals, there were significant increases in body weight, ejaculate volume and plasma testosterone during the
breeding season. With the exception of one animal, there was also a decrease in ejaculation latency during the season. Seasonal
differences in the sperm count and sperm motility were not observed. Testosterone-implanted castrates showed changes in both
ejaculate volume and ejaculation latency similar to those seen in intact monkeys during the breeding season. The body weight
and plasma testosterone of the castrates remained quite constant throughout the year.
Supported by NIH grants HD 00778, MH 21178 and MH 23645. 相似文献
103.
Arlette Acoutte-Panvier Julian E. Davies Linda R. Gritz Barbara S. Littlewood 《Molecular & general genetics : MGG》1980,179(2):273-282
Summary The cytoplasmic ribosomal proteins (r-proteins) of seventeen yeast species of the genera Saccharomyces and Kluyveromyces were analyzed by one-dimensional gradient polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. The electrophoretic patterns of cytoplasmic r-proteins from different species display extensive differences in both the 40S and the 60S subunit. Relatedness of species suggested by r-protein patterns correlates well with that based on DNA/DNA homology (Bicknell and Douglas 1970). Immunochemical cross-reactions and antibiotic susceptibility tests were also used to compare different species.Analyses of r-proteins from two different interspecific hybrids showed that their ribosomes were hybrid, containing r-proteins from both parents. These findings are discussed in relation to the evolution of yeast species and the regulation of expression of r-proteins in cucaryotes. 相似文献
104.
Eugenia mcvaughii is described from a forest remnant of the Jardin Botánico of Caracas, Venezuela. Found also in the hills adjacent to Caracas, it may be considered as an endemic species of the Interior Coastal Cordillera. 相似文献
105.
A K Grover C Y Kwan J Crankshaw E E Daniel 《Canadian journal of physiology and pharmacology》1981,59(11):1128-1133
Isopycnic centrifugation experiments using sucrose density gradients showed that in digitonin-treated microsomes the distribution of the plasma membrane (PM) marker 5'-nucleotidase was shifted to higher densities. The treatment also caused similar but less pronounced changes in the distribution of protein, the putative endoplasmic reticulum (ER) marker NADPH-dependent cytochrome c reductase, and the inner mitochondrial marker cytochrome c oxidase. Similar experiments using more purified membrane fractions showed that the digitonin treatment led to a comparable increase in the densities of the fractions N1 and N2 previously described as subfractions of plasma membrane and to considerably less increase in the density of the fraction N3B which is enriched in the endoplasmic reticulum and the inner mitochondrial markers. Digitonin inhibited the ATP-dependent Ca uptake by the N1 fraction in a concentration-dependent manner (I50 = 0.3 mg/mL). Digitonin (0.5 mg/mL) inhibited the ATP-dependent azide-insensitive Ca uptake by all the fractions. The results support the hypothesis that (a) N1 and N2 are subfractions of plasma membrane, and (b) ATP-dependent azide-insensitive Ca uptake in rat myometrium is a property of plasma membranes. 相似文献
106.
The effects of caffeine, thymol, and procaine on calcium release from fragmented sarcoplasmic reticulum (FSR) from rabbit skeletal white muscle were investigated by the spin label method at the organellar level. Two thiol-directed spin labels, 4-maleimide-2,2,6,6-tetramethylpiperidinooxyl and 4-(2-iodoacetamide)-2,2,6,6-tetramethylpiperidinooxyl, were used for the labeling of SR proteins. The ratio (W/S) of the weakly (W) and strongly (S) immobilized ESR signals was measured for the maleimide and iodoacetamide labeled FSR. The two labels gave different W/S values, which means that the two labels report conformational changes at different loci of SR proteins. The dependences of the W/S ratios on the concentration of the drugs showed that conformational changes of SR proteins induced by these drugs are not the same. From measurements of the distribution of 5-doxyldecanoic acid methylester between the lipid and water phases, it was found that the conformational changes of the SR proteins caused by thymol or procaine induced a disorder in local regions of the phospholipid bilayers of FSR, while such disordering was not induced by caffeine. On the other hand, caffeine and thymol showed definite effects on calcium release from FSR, while procaine did not. These results indicate that the effects of the drugs on the protein conformations can be well characterized at the organellar level by means of the spin label technique and that some specific changes in the conformations of SR proteins are necessary for calcium release from FSR. 相似文献
107.
Julian A. Steyermark 《Brittonia》1980,32(1):17-23
Three new species,Lubaria szczerbanii (Rutaceae),Croton guaiquinimae (Euphorbiaceae), andStomatochaeta colveei (Asteraceae), are described from the summit of Cerro Guaiquinima, Venezuela. The generic affinities betweenLubaria andMyllanthus, and betweenStomatochaeta andStenopadus are discussed. 相似文献
108.
Extracellular recordings were made of single neurons in precentral cortex of awake monkeys. These neurons were somatotopically identified with respect to their responses to inputs from single joints or their somatic surround. Many of these neurons exhibited early (less than 50 ms) and late (greater than 50 ms) discharges in response to flexion or extension torques delivered about the wrist. With the monkey in a mode requiring opposition to the injected torque, all responsive neurons showed a parallel excitatory or inhibitory modification in the early and late discharges. This was true both for cells identified as wrist (flexion-extension) neurons and those identified as nonwrist (flexion-extension) neurons. These findings indicate that the reflex and voluntary components of percentral discharge invariably show a congruent functional response to a torque disturbance, for this particular instruction set. 相似文献
109.
Multilayer planar membranes applicable to ion-transport measurements were constructed from egg yolk lecithin, egg yolk lecithin-cholesterol mixture, and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine between two tightly stretched cellulose sheets. While most of the phospholipids in the membranes were found by a spin label technique to be uniformly oriented with their long hydrocarbon chains perpendicular to the surfaces of the cellulose sheets, a small fraction of phospholipids were isotropically oriented in multilayer membranes. The amount of phospholipids with isotropic orientations decreased with increasing content of cholesterol in membranes and became zero in membranes of egg yolk lecithin-cholesterol mixture (molar ratio of 1: 0.67). The degree of orientation, S, of uniformly oriented phospholipids in membranes was also increased by adding cholesterol to the membranes. The orientation of phospholipids in membranes was rather stable in distilled water and in aqueous calcium chloride (1, 10, 100 mM), while a marked disordering of oriented phospholipids was induced in a aqueous solutions containing thymol, isopropanol, or butanol beyond certain specific concentrations. The membranes can be used for measurements of calcium permeation. An appreciable barrier function to calcium permeation was detected with these multilayer planar membranes as compared with control experiments using only cellulose sheets as membranes. A preliminary investigation suggested that changes in the orientational structure of phospholipids in the multilayer planar membranes are correlated with permeability properties of the membranes. 相似文献
110.
Julian A. Steyermark 《Brittonia》1978,30(1):39-49
Ten new species (Billbergia manarae, Croizatia naiguatensis, Croton huberi, Rinorea oraria, Anaectocalyx manarae, Linociera avilensis, Cynanchum beatricis, C. manarae, Matelea costanensis, and M. manarae) are described in preparation for the forthcoming Flora of Avila and Naiguatá. 相似文献