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91.
Summary Ghosts of human erythrocytes prepared by hypotonic hemolysis were assayed for aldolase, triosephosphate isomerase, glyceraldehyde phosphate dehydrogenase, phosphoglycerate kinase, pyruvate kinase, lactate dehydrogenase, and glutathione peroxidase and reductase. Cryptic activity of the enzymes was demonstrated by an increase in activity on dilution with water, which caused fragmentation of the ghosts. Aldolase and glyceraldehyde phosphate dehydrogenase were classed as firmly bound; phosphoglycerate kinase was intermediate; the others were loosely bound. Triton X-100 increased the activities of aldolase, glyceraldehyde phosphate dehydrogenase, and phosphoglycerate kinase. The pH of the medium had little effect upon the firmly bound enzymes but it markedly affected the retention of hemoglobin and the activities of the loosely bound enzymes. The presence of Mg or Ca ions enhanced the retention of hemoglobin and the activity of lactate dehydrogenase and pyruvate kinase, with little effect on aldolase and glyceraldehyde phosphate dehydrogenase. Ghosts diluted in water disintegrated into fragments and tubules or vesicles; Mg or Ca at 1mm afforded protection against this. When ghosts were treated with Triton X-100 and adenosine triphosphate, they contracted to about one-seventh of their volume. The shrunken ghosts had lost a considerable proportion of their cholesterol and protein to the medium. 相似文献
92.
Antiserum was made against a single 30S protein, 30S-7. The amount of complement fixed by total 30S protein in the presence of this antiserum indicated that protein 30S-7 was the major antigen in the mixture of proteins. Each of the 30S ribosomal proteins was tested for cross-reactivity with anti-30S-7. This was done by determining if any of the other 30S proteins inhibited complement fixation by 30S-7. None of the other 30S proteins was found to inhibit complement fixation by 30S-7, indicating that 30S-7 is antigenically distinct from the other proteins. 相似文献
93.
Victor G. Bruce 《Genetics》1974,77(2):221-229
Mutants affecting the period length of the biological clock in Chlamydomonas reinhardi have been isolated and a start has been made on analyzing the genetics of this system. In four mutants, the long period characteristic seems to be controlled by single genes at separate loci. Crosses between single mutants, as well as crosses involving three or four mutant genes, yielded progeny with periods characteristic of the parents as well as recombinant types, including normal period (wild type) and extra-long periods (double, triple and quadruple mutants). It was found that the period lengthening effect is additive; that is, the period of double mutants is lengthened by the sum of the period lengthening of the single mutants. 相似文献
94.
A comparison of wild-type and mutant ribitol dehydrogenases from Klebsiella aerogenes 总被引:6,自引:1,他引:5 下载免费PDF全文
Bruce D. Burleigh Jr. Peter W. J. Rigby Brian S. Hartley 《The Biochemical journal》1974,143(2):341-352
A ribitol dehydrogenase (ribitol-NAD(+) oxidoreductase, EC. 1.1.1.56) having increased specificity and catalytic efficiency toward xylitol was isolated from mutant strains of Klebsiella aerogenes, which were selected for increased growth rate on xylitol over the ribitol dehydrogenase constitutive wild-type organism. 2. The mutant enzyme was purified to homogeneity and its general characteristics were compared with those of the previously purified wild-type enzyme. 3. Initial-velocity steady-state kinetic parameters were determined for both wild-type and mutant enzymes and the results compared. 4. The results are interpreted in terms of a model in which the mutant enzyme results from a small change of amino acid sequence, which affects both the stability and conformational equilibria of the molecule. 相似文献
95.
CHROMOSOME MICROMANIPULATION : III. Spindle Fiber Tension and the Reorientation of Mal-Oriented Chromosomes 总被引:7,自引:4,他引:3 下载免费PDF全文
Kinetochore reorientation is the critical process ensuring normal chromosome distribution. Reorientation has been studied in living grasshopper spermatocytes, in which bivalents with both chromosomes oriented to the same pole (unipolar orientation) occur but are unstable: sooner or later one chromosome reorients, the stable, bipolar orientation results, and normal anaphase segregation to opposite poles follows. One possible source of stability in bipolar orientations is the normal spindle forces toward opposite poles, which slightly stretch the bivalent. This tension is lacking in unipolar orientations because all the chromosomal spindle fibers and spindle forces are directed toward one pole. The possible role of tension has been tested directly by micromanipulation of bivalents in unipolar orientation to artificially create the missing tension. Without exception, such bivalents never reorient before the tension is released; a total time "under tension" of over 5 hr has been accumulated in experiments on eight bivalents in eight cells. In control experiments these same bivalents reoriented from a unipolar orientation within 16 min, on the average, in the absence of tension. Controlled reorientation and chromosome segregation can be explained from the results of these and related experiments. 相似文献
96.
Summary Negative staining showed the presence of microcrystals in various polysaccharides. Cellulose microcrystals from Valoniopsis, Vaucheria, and an unidentified tunicate had widths of 20, 27, and 30 Å, respectively. Mannan microcrystals from Acetabularia were 10x25 Å and were oriented in linear arrays with their long axis perpendicular to the array axis. dichotomosiphon and Caulerpa xylans had respective microcrystal widths of 22 and 24 Å. All microcrystals appeared as component part of microfibrils. 相似文献
97.
Each major component of the proteins of 30S ribosomes from Escherichia coli was compared with the proteins of 50S ribosomes. The comparisons were done by using polyacrylamide gel electrophoresis in urea with differentially labeled proteins. The data show that no major protein is common to both ribosomes. 相似文献
98.
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