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441.
Enzymic reaction velocities often depend primarily on the concentrations of single free and complexed species rather than on the total metal and metabolite concentrations. For determining single species concentrations from total concentrations and complex stability constants, a program is described. The program may not only calculate the single concentrations, but also estimate their uncertainty due to the unavoidable uncertainty of complex stability constants. Making use of the ICT 1900 magnetic drum storage, it may deal with quite large complex patterns as are found in vivo. 相似文献
442.
The heterotrophically grown, mutant No. 8 of Scenedesmus obliquus is unable to carry out photosynthesis. Yet, chloroplast particles isolated from the alga reduced ferricyanide. They also reduced methyl viologen in the presence of the artificial donor reduced 2,6-dichlorophenol indophenol with a low yield but an appreciable saturation rate. NADP reduction or turn-over could not be detected.When grown mixotrophically, the mutant showed increasing activity with a concomitant increase in the rate of photosynthesis. Both activities were lost again when the algae were returned to darkness. Isolated chloroplast particles showed a good turn-over and reasonable rates of NADP reduction.The data suggest that the mutation occurred at a site preceding the formation of the pigment. The results on the photochemical activities are discussed in the light of reports concerning the involvement of in linear electron transport. 相似文献
443.
444.
Membrane attach complex of complement (MAC): three-dimensional analysis of MAC-phospholipid vesicle recombinants 总被引:3,自引:0,他引:3
E R Podack H J Müller-Eberhard H Horst W Hoppe 《Journal of immunology (Baltimore, Md. : 1950)》1982,128(5):2353-2357
The three-dimensional structure of recombinants of the isolated membrane attack complex (MAC) of complement with single bilayer dioleoyllecithin (DOL) vesicles and with dimyristoyllecithin (DML) vesicles was determined. A total of four MAC-vesicle complexes were analyzed by imaging negatively stained specimens at various defined tilting angles under minimal dose conditions in the electron microscope and by computer-aided three-dimensional reconstruction. The information on electron micrographs obtained at 6 degrees angular increments from +60 degrees to -60 degrees was digitized by densitometric scanning, Fourier-transformed, corrected for imaging errors, cross-correlated, and synthesized to the three-dimensional image. All four MAC-vesicle recombinants showed stain penetration into the interior of the vesicle, indicating increased permeability of the bilayer to negative stain. The MAC appeared as a hollow structure of 16-nm height, 2.0-nm wall thickness, and a 3.0-nm torus at the free end with an outer and inner diameter of 20.0 nm and 10.0 nm. In MAC-DOL vesicles the hollow core of the MAC terminated at the membrane-binding site, and only small pores of up to 2.0-nm in diameter penetrated the bilayer. In one MAC-DML vesicle lipid discontinuities on the outer circumference of the MAC binding site mediated stain penetration. The second MAC-DML vesicle showed a channel of approximately 4.0 nm connecting the hollow core of the MAC across the bilayer with the vesicle interior. The results suggest the MAC may mediate increased membrane permeability by protein channel formation in addition to lipid reorientation. 相似文献
445.
U Petzoldt G R Illmensee K B?rki P C Hoppe K Illmensee 《Molecular & general genetics : MGG》1981,184(1):11-16
Summary In order to compare paternal and maternal gene activity at the protein synthesis level during early development, androgenetic and gynogenetic mouse embryos were experimentally produced by microsurgically removing either the female or the male pronucleus from fertilized mouse eggs. The resulting haploid eggs were diploidized in a medium containing cytochalasin B and then cultured under normal conditions to the blastocyst stage. Protein synthesis was analyzed at different stages of preimplantation development using 2-dimensional polyacrylamide gel electrophoresis. Both types of uniparental embryos synthesized a similar set of proteins independent of whether the paternal or the maternal genome was present. The isodiploid embryos expressed a protein pattern that corresponded remarkably to normal embryos at the subsequent cleavage stage. This temporal change is probably due to the fact that the operated haploid eggs were kept overnight in cytochalasin B in order to allow chromosomal replication to occur without cell division, and the resulting eggs therefore corresponded to normal 2-cell embryos with respect to karyokinesis but differed as far as cytokinesis was concerned. Several 2-cell specific proteins appeared in these isodiploid eggs and, similarly, following their first cleavage some 4-cell specific proteins were detected in 2-cell androgenetic and gynogenetic embryos. The discordance between nuclear and cellular division, which was retained through the 4-cell stage, however disappeared during subsequent cleavage divisions. At the blastocyst stage, both kinds of uniparental embryos showed a similar protein pattern compared to normal embryos. Our data suggest that some stage-specific proteins are synthesized during preimplantation development and correspond to nuclear rather than cellular divisions.Some of these results were presented at the 13th Annual Meeting of the Union of Swiss Societies of Experimental Biology in Lausanne, March 1981 (Petzoldt et al. 1981) 相似文献
446.
The effect of relaxed functional constraints on the photosynthetic gene rbcL in photosynthetic and nonphotosynthetic parasitic plants 总被引:1,自引:0,他引:1
The photosynthetic gene rbcL has been lost or dramatically altered in some
lineages of nonphotosynthetic parasitic plants, but the dynamics of these
events following loss of photosynthesis and whether rbcL has sustained
functionally significant changes in photosynthetic parasitic plants are
unknown. To assess the changes to rbcL associated with the loss of
functional constraints for photosynthesis, nucleotide sequences from
nonparasitic and parasitic plants of Scrophulariales were used for
phylogeny reconstruction and character analysis. Plants in this group
display a broad range of parasitic abilities, from photosynthetic
("hemiparasites") to nonphotosynthetic ("holoparasites"). With the
exception of Conopholis (Orobanchaceae), the rbcL locus is present in all
parasitic plants of Scrophulariales examined. Several holoparasitic genera
included in this study, including Boschniakia, Epifagus, Orobanche, and
Hyobanche, have rbcL pseudogenes. However, the holoparasites Alectra
orobanchoides, Harveya capensis, Harveya purpurea, Lathraea clandestina,
Orobanche corymbosa, O. fasciculata, and Striga gesnerioides have intact
open reading frames (ORFs) for the rbcL gene. Phylogenetic hypotheses based
on rbcL are largely in agreement with those based on sequences of the
nonphotosynthetic genes rps2 and matK and show a single origin of
parasitism, and loss of photosynthesis and pseudogene formation have been
independently derived several times in Scrophulariales. The mutations in
rbcL in nonparasitic and hemiparasitic plants would result in largely
conservative amino acid substitutions, supporting the hypothesis that
functional proteins can experience only a limited range of changes, even in
minimally photosynthetic plants. In contrast, ORFs in some holoparasites
had many previously unobserved missense substitutions at functionally
important amino acid residues, suggesting that rbcL genes in these plants
have evolved under relaxed or altered functional constraints.
相似文献
447.
J. C. Crause J. A. Verschoor J. Coetzee H. C. Hoppe J. N. Taljaard R. Gothe A. W. H. Neitz 《Experimental & applied acarology》1993,17(5):357-363
A monoclonal antibody directed against a paralysis toxin of Rhipicephalus evertsi evertsi ticks was used to localize the toxin in cytoplasmic granules and, surprisingly, chromatin of the nuclei of cells which resemble the b cell type in the salivary glands of Rhipicephalus appendiculatus, Boophilus microplus and Ixodes holocyclus. The association of toxin with chromatin indicates that the toxin may have a regulatory function. Evidence is provided to support the view that the toxin is made up of three identical sub-units, with only the trimeric form being toxic. 相似文献
448.
Influence of sex of the transmitting parent as well as of parental allele site on the CTG expansion in myotonic dystrophy (DM)
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H. G. Brunner H. T. Brüggenwirth W. Nillesen G. Jansen B. C. J. Hamel R. L. E. Hoppe C. E. M. de Die C. J. Hweler B. A. van Oost B. Wieringa H. H. Ropers H. J. M. Smeets 《American journal of human genetics》1993,53(5):1016-1023
In patients with myotonic dystrophy (DM), the severity of clinical signs is correlated with the length of a (CTG)n trinucleotide repeat sequence. This sequence tends to expand in subsequent generations. In order to examine the kinetics of this process and, in particular, the influence of the mutant-allele size and the sex of the transmitting parent, we have studied (CTG)n repeat lengths in the offspring of 38 healthy carriers with small mutations (less than 100 CTG trinucleotides, mean length [CTG]67). In these studies, we found a weakly positive correlation between the size of the mutation in the carrier parents and that in their offspring. Furthermore, we observed that, in the offspring of male transmitters, repeat lengths exceeding 100 CTG trinucleotides were much more frequent than in the offspring of carrier females (48 [92%] of 52 vs. 7 [44%] of 16, P = .0002). Similarly, in genealogical studies performed in 38 Dutch DM kindreds, an excess of nonmanifesting male transmitters was noted, which was most conspicuous in the generation immediately preceding that with phenotypic expression of DM. Thus, two separate lines of evidence suggest that the sex of the transmitting parent is an important factor that determines DM allele size in the offspring. On the basis of our data, we estimate that when both parents are asymptomatic, the odds are approximately 2:1 that the father carries the DM mutation. Because expansion of the CTG repeat is more rapid with male transmission, negative selection during spermatogenesis may be required to explain the exclusive maternal inheritance of severe congenital onset DM. 相似文献
449.
Preparation of biologically active platelet-derived growth factor type BB from a fusion protein expressed in Escherichia coli 总被引:5,自引:0,他引:5
Preparations of the mitogen platelet-derived growth factor (PDGF) from human platelets contain two related polypeptides termed A chain and B chain. PDGF-B is highly homologous to a portion of p28v-sis, the transforming protein of simian sarcoma virus. We have studied the mitogenic potential of a PDGF-BB-like homodimer by expressing the sequence coding for the mature part of PDGF-B in Escherichia coli. Expression was achieved as cro-beta-gal-PDGF-B fusion protein which was exclusively found in the "inclusion bodies". A monomeric PDGF-B fragment shortened by 12 amino acid residues from the NH2 terminus was excised from the fusion protein by CNBr cleavage. After protection of thiols by S-sulfonation, this fragment was purified by gel permeation chromatography and reversed-phase high-performance liquid chromatography. This monomeric protein was dimerized in the presence of a mixture of reduced and oxidized glutathione to yield biologically active rPDGF-BB with an overall yield of approximately 0.7 mg of rPDGF-BB/L of culture. Escherichia coli rPDGF-BB stimulated [3H]thymidine incorporation into AKR2B fibroblast at concentrations of about 1 ng/mL. 相似文献
450.
Sequence of subunit c of the sodium ion translocating adenosine triphosphate synthase of Propionigenium modestum 总被引:1,自引:0,他引:1
W Ludwig G Kaim W Laubinger P Dimroth J Hoppe K H Schleifer 《European journal of biochemistry》1990,193(2):395-399
The 30 N-terminal amino acid residues of the purified ATPase c subunit of Propionigenium modestum have been determined. An oligonucleotide mixture was derived from this sequence and used as probe for cloning the corresponding gene in Escherichia coli. The nucleotide sequence of the gene has been determined and compared with those of ATPase c subunits from other bacteria and chloroplasts. Peculiar sequence similarities are found only at the C-terminus between the c subunits of the ATPases from P. modestum and from Vibrio alginolyticus, another putative Na(+)-translocating ATPase. 相似文献