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31.
Metal Ion Interactions with Phosphoenolpyruvate Carboxylase from Crassula argentea and Zea mays 总被引:1,自引:1,他引:0
Metal ion interactions with phosphoenolpyruvate carboxylase from the CAM plant Crassula argentea and the C4 plant Zea mays were kinetically analyzed. Fe2+ and Cd2+ were found to be active metal cofactors along with the previously known active metals Mg2+, Mn2+, and Co2+. In studies with the Crassula enzyme, Mg2+ yielded the highest Vmax value but also generated the highest values of Km(metal) and Km(pep). For these five active metals lower Km(metal) values tended to be associated with lower Km(pep) values. PEP saturation curves showed more kinetic cooperativity than the corresponding metal saturation curves. The activating metal ions all have ionic radii in the range of 0.86 to 1.09 Å. Ca2+, Sr2+, Ba2+, and Ni2+ inhibited competitively with respect to Mg2+, whereas Be2+, Cu2+, Zn2+, and Pd2+ showed mixed-type inhibition. Vmax trends with the five active metals were similar for the C. argentea and Z. mays enzymes except that Cd2+ was less effective with the maize enzyme. Km(metal) values were 10- to 60-fold higher in the enzyme from Z. mays. 相似文献
32.
Effect of gamma radiation on resting B lymphocytes. II. Functional characterization of the antigen-presentation defect 总被引:4,自引:0,他引:4
J D Ashwell M K Jenkins R H Schwartz 《Journal of immunology (Baltimore, Md. : 1950)》1988,141(8):2536-2544
The effect of radiation on three discrete Ag-presentation functions in resting B cells was examined: 1) Ag uptake and processing, 2) expression of processed Ag in the context of functional class II molecules, and 3) provision of necessary co-stimulatory, or "second," signals. Analysis of radiation's effect on B cell presentation of intact vs fragmented Ag or its effect on presentation by Ag-pulsed B cells indicated that damage to Ag uptake and processing could not account for the bulk of the radiation-induced Ag-presentation defect. Experiments with phosphatidylinositol hydrolysis as an indirect measure of TCR occupancy suggested that irradiation caused a fairly rapid (within 1 to 2 h) decrease in the ability of the B cell APC to display a stimulatory combination of Ag and class II molecule. Ag dose-response analyses demonstrated that when presenting a fragment of the Ag pigeon cytochrome c to a T cell clone, 3000 rad-treated B cell APC were able to stimulate approximately 50% as much phosphatidylinositol turnover as unirradiated B cells. It was also found that, in contrast to their inability to initiate T cell proliferation, and similarly to chemically cross-linked splenocytes, heavily irradiated resting B cells plus Ag induced a state of Ag hyporesponsiveness in T cell clones. This effect on T cells had the same Ag- and MHC-specificity as did receptor occupancy required for proliferation, indicating that heavily irradiated resting B cells bear functional class II molecules. Co-culture of T cells with allogeneic B cells and syngeneic heavily irradiated B cells or chemically cross-linked splenic APC plus Ag resulted in T cell proliferation and interfered with the induction of the hyporesponsive state. This co-stimulatory function was radiosensitive in resting allogeneic B cells. Together, these data support the hypothesis that the major functional consequences of radiation to resting B cell APC are a reduction in the effective display of Ag plus class II molecules and, probably what is more important, a loss in the ability to provide APC-derived co-stimulatory signals. 相似文献
33.
Michael J. Jenkins James Sneyd Scott Camazine J. D. Murray 《Journal of mathematical biology》1992,30(3):281-306
We present a simplified version of a previously presented model (Camazine et al. (1990)) that generates the characteristic
pattern of honey, pollen and brood which develops on combs in honey bee colonies. We demonstrate that the formation of a band
of pollen surrounding the brood area is dependent on the assumed form of the honey and pollen removal terms, and that a significant
pollen band arises as the parameter controlling the rate of pollen input passes through a bifurcation value. The persistence
of the pollen band after a temporary increase in pollen input can be predicted from the model. We also determine conditions
on the parameters which ensure the accumulation of honey in the periphery and demonstrate that, although there is an important
qualitative difference between the simplified and complete models, an analysis of the simplified version helps us understand
many biological aspects of the more complex complete model.
Corresponding author 相似文献
34.
35.
K J Moore M A D'Amore-Bruno T R Korfhagen S W Glasser J A Whitsett N A Jenkins N G Copeland 《Genomics》1992,12(2):388-393
Pulmonary surfactant, a protein-phospholipid mixture, maintains surface tension at the lung epithelium/air interface preventing alveolar collapse during respiration. For mammals appropriate developmental production of surfactant is necessary for adaptation to the air breathing environment. Deficiency of pulmonary surfactant results in respiratory distress syndrome (RDS), a leading cause of death in premature infants. Recently, three lung-specific pulmonary surfactant proteins designated SP-A, SP-B, and SP-C have been described. Cloned sequences for the genes that encode each of these proteins have been partially characterized in humans and other species. Analysis of interspecific backcross mice has allowed us to map the chromosomal locations of these three genes in the mouse. The gene encoding SP-A (Sftp-1) and the gene encoding SP-C (Sftp-2) both map to mouse chromosome 14, although at separate locations, while the gene encoding SP-B (Sftp-3) maps to chromosome 6. The mouse map locations determined in this study for the Sftp genes are consistent with the locations of these genes on the human genetic map and the syntenic relationships between the human and the mouse genomes. 相似文献
36.
S E Spence D J Gilbert B S Harris M T Davisson N G Copeland N A Jenkins 《Genomics》1992,12(2):403-404
The blind-sterile (bs) mutation in the mouse was localized on Chromosome 2 between Hao-1 and Emv-13. N2 progeny from a backcross between congenic female 129.AKR-bs Emv-13 mice and (129.AKR-bs/bs x Mus musculus molossinus) F1 male mice were typed by analysis of isozyme variants for Hao-1, visible inspection for bs, and restriction fragment length polymorphism for Emv-13 and Emv-15. Comparison between markers on mouse Chromosome 2 and corresponding markers on human chromosomes suggest that the human homolog of bs will be located on 20q11-q13. 相似文献
37.
Camilynn I. Brannan Debra J. Gilbert Jeffrey D. Ceci Yoichi Matsuda Verne M. Chapman John A. Mercer Harvey Eisen Laura A. Johnston Neal G. Copeland Nancy A. Jenkins 《Genomics》1992,13(4):1075-1081
We have used an interspecific backcross between C57BL/6J and Mus spretus to derive a molecular genetic linkage map of chromosome 15 that includes 25 molecular markers and spans 93% of the estimated length of chromosome 15. Using a second interspecific backcross that was analyzed with a centromere-specific marker, we were also able to position our map with respect to the chromosome 15 centromere. This map provides molecular access to many discrete regions on chromosome 15, thus providing a framework for establishing relationships between cloned DNA markers and known mouse mutations and for identifying homologous genes in mice and humans that may be involved in disease. 相似文献
38.
Monica J. Justice Bebra J. Gilbert Kenneth W. Kinzler Bert Vogelstein Authur M. Buchberg Jeffrey D. Ceci Yoichi Matsuda Verne M. Chapman Christos Patriotis Antonios Makris Philip N. Tsichlis Nancy A. Jenkins Neal G. Copeland 《Genomics》1992,13(4):1281-1288
An interspecific backcross between C57BL/6J and Mus spretus was used to generate a molecular genetic linkage map of mouse chromosome 18 that includes 23 molecular markers and spans approximately 86% of the estimated length of the chromosome. The Apc, Camk2a, D18Fcr1, D18Fcr2, D18Leh1, D18Leh2, Dcc, Emb-rs3, Fgfa, Fim-2/Csfmr, Gnal, Grl-1, Grp, Hk-1rs1, Ii, Kns, Lmnb, Mbp, Mcc, Mtv-38, Palb, Pdgfrb, and Tpl-2 genes were mapped relative to each other in one interspecific backcross. A second interspecific backcross and a centromere-specific DNA satellite probe were used to determine the distance of the most proximal chromosome 18 marker to the centromere. The interspecific map extends the known regions of linkage homology between mouse chromosome 18 and human chromosomes 5 and 18 and identifies a new homology segment with human chromosome 10p. It also provides molecular access to many regions of mouse chromosome 18 for the first time. 相似文献
39.
Hematopoietic cell phosphatase (Hcph) was identified by amplification of conserved protein tyrosine phosphatase sequences from a myeloid cell line and is predominantly expressed in hematopoietic cells. Hcph is unique in containing two, tandemly repeated, src-homology 2 domains in the amino terminal region of the phosphatase. Using a genomic probe in interspecific backcross analysis, the murine Hcph gene maps to mouse Chromosome 6 and is tightly linked to the Tnfr-2 and Ly-4 genes. 相似文献
40.