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1.
Chemical modification of spinach plastocyanin using 4-chloro-3,5-dinitrobenzoic acid: characterization of four singly-modified forms 总被引:2,自引:0,他引:2
Chemical modification of plastocyanin was carried out using 4-chloro-3,5-dinitrobenzoic acid, which has the effect of replacing positive charges on amino groups with negatively charged carboxyl groups. Four singly-modified forms were obtained which were separated using anion exchange FPLC. The four forms were modified at the N-terminal valine and at lysines 54, 71 and 77. The rates of reaction with mammalian cytochrome c were increased for all four modified plastocyanins. In contrast, the rates of reaction with cytochrome f were inhibited for the forms modified at residues 1, 54 and 77, whereas no effect was observed for the form modified at residue 71. Modification had no effect on either the midpoint redox potential or the reaction with K3Fe(CN)6. These results are consistent with a model in which charged residues on plastocyanin located at or near the binding site for cytochrome f recognize the positively-charged binding site on cytochrome f. In contrast, charged residues located at points on plastocyanin distant from the cytochrome f binding site recognize the net negative charge on the cytochrome f molecule. Based on these considerations, Glu-68 may be within the interaction sphere of cytochrome f, suggesting that cytochrome f may donate electrons to plastocyanin at either Tyr-83 or His-87. 相似文献
2.
Maintenance of the cellobiose utilization genes of Escherichia coli in a cryptic state 总被引:6,自引:1,他引:5
The genes for cellobiose utilization are normally cryptic in Escherichia
coli. The cellobiose system was used as a model to understand the process
by which silent genes are maintained in microbial populations. Previously
reported was (1) the isolation of a mutant strain that expresses the
cellobiose-utilization (Cel) genes and (2) that expression of those genes
allows utilization of three beta- glucoside sugars: cellobiose, arbutin,
and salicin. The Cel gene cluster has now been cloned from that mutant
strain. In the course of locating the Cel genes within the cloned DNA
segment, it was discovered that inactivation of the Cel-encoded hydrolase
rendered the host strain sensitive to all three beta-glucosides as potent
inhibitors. This sensitivity arises from the accumulation of the
phosphorylated beta- glucosides. Because even the fully active genes
conferred some degree of beta-glucoside sensitivity, the effects of
cellobiose on a series of five Cel+ mutants of independent origin were
investigated. Although each of those strains utilizes cellobiose as a sole
carbon and energy source, cellobiose also acts as a potent inhibitor that
reduces the growth rate on glycerol 2.5-16.5-fold. On the other hand,
wild-type strains that cannot utilize cellobiose are not inhibited. The
observation that the same compound can serve either as a nutrient or as an
inhibitor suggests that, under most conditions in which cellobiose will be
present together with other resources, there is a strong selective
advantage to having the cryptic (Cel0) allele. In those environments in
which cellobiose is the sole, or the best, resource, mutants that express
the genes (Cel+) will have a strong selective advantage. It is suggested
that temporal alternation between these two conditions is a major factor in
the maintenance of these genes in E. coli populations. This alternation of
environments and fitnesses was predicted by the model for cryptic-gene
maintenance that was previously published.
相似文献
3.
Selection-induced mutations are nonrandom mutations that occur as specific
and direct responses to environmental challenge. Examples of
selection-induced mutations have been reported both in bacteria and in
yeast. I previously showed (Hall 1988) that excisions of the mobile genetic
element IS150 from within bglF are selection induced and argued that they
occurred because they were potentially advantageous under the selective
conditions employed. Mittler and Lenski (Mittler and Lenski 1992) have
argued that such excisions are not selection induced but that they occur
randomly in nondividing cells. Here I provide further evidence that IS150
excisions are induced by selection and that the excisions are immediately,
rather than only potentially, advantageous to the cell. I also provide
evidence that excisions, which Mittler and Lenski claim occur randomly in
saturated broth cultures, actually occur after samples from those cultures
are plated onto selective medium.
相似文献
4.
By comparing the shells of those mussels Mytilus edulis that had been opened by oystercatchers Haematopus ostralegus with mussels of similar size that had not been opened, it was shown that oystercatchers that break into their prey by hammering a hole in the shell selected between prey within a size-class. Ventral hammerers selected mussels that were relatively thin on the ventral surface, were brown in colour and carried few barnacles. Dorsal hammerers selected eroded mussels with thin dorsal shells. Stabbing oystercatchers did not select for thin-shelled prey. In conjunction with the great individual variation in flesh content between mussels of the same length, prey size in this case can be only a poor predictor of prey profitability. 相似文献
5.
Atomic-scale computer models were developed for how cecropin peptides may assemble in membranes to form two types of ion channels. The models are based on experimental data and physiochemical principles. Initially, cecropin peptides, in a helix-bend-helix motif, were arranged as antiparallel dimers to position conserved residues of adjacent monomers in contact. The dimers were postulated to bind to the membrane with the NH2-terminal helices sunken into the head-group layer and the COOH-terminal helices spanning the hydrophobic core. This causes a thinning of the top lipid layer of the membrane. A collection of the membrane bound dimers were then used to form the type I channel structure, with the pore formed by the transmembrane COOH-terminal helices. Type I channels were then assembled into a hexagonal lattice to explain the large number of peptides that bind to the bacterium. A concerted conformational change of a type I channel leads to the larger type II channel, in which the pore is formed by the NH2-terminal helices. By having the dimers move together, the NH2-terminal helices are inserted into the hydrophobic core without having to desolvate the charged residues. It is also shown how this could bring lipid head-groups into the pore lining. 相似文献
6.
Atomic scale structure and functional models of voltage-gated potassium channels. 总被引:6,自引:0,他引:6 下载免费PDF全文
Recent mutagenesis experiments have confirmed our hypothesis that a segment between S5 and S6 forms the ion selective portion of voltage-gated ion channels. Based on these and other new data, we have revised previous models of the general folding pattern of voltage-gated channel proteins and have developed atomic scale models of the entire transmembrane region of the Shaker A K+ channel. In these models, the ion selective region is a beta-barrel that spans the outer half of the membrane. The inner half of the pore is larger. The voltage-dependent conformational changes of activation gating are modeled to occur by the "helical screw" mechanism, in which the four S4 segments move along and rotate about their axes. These changes are followed by a voltage-independent conformational change, in which the segments linking S4 to S5 move from blocking the intracellular entrance of the pore to forming part of the lining of the large inner portion of the pore. The NH2-terminal of the protein was modeled as an alpha-helix that plugs the intracellular half of the pore to inactivate the channel. 相似文献
7.
Durell DL Pujol TJ Barnes JT 《Journal of strength and conditioning research / National Strength & Conditioning Association》2003,17(2):368-373
The purpose of this study was to determine the extent to which scientific research influences college strength and conditioning coaching practices and to determine the training methods utilized. A total of 321 surveys were mailed to Division I strength and conditioning coaches, and the response rate was 42.7% (137 of 321 surveys). Results indicate that all subjects held a baccalaureate degree, the majority in a human performance-related field, and that 75% were Certified Strength and Conditioning Specialist (CSCS) certified. The respondents' most widely utilized professional resources were the Strength and Conditioning Journal (94%) and other collegiate coaches and programs (93%). Forty-seven percent of respondents indicated that other collegiate coaches and their programs were the most important sources of knowledge outside of formal education. The majority indicated that they used a periodization protocol (93%) utilizing multiple sets (97%), plyometrics (90%), explosive movements (88%), and Olympic lifts (85%). Respondents tend to rely on sources of information that may not be defined as scientific, as evidenced by the low priority given to peer-reviewed literature. Respondents also tend to employ the methods they utilized as athletes. Reliance on these sources may not take advantage of advances made through scientific research in exercise physiology, biomechanics, and more specifically the area of strength and conditioning. 相似文献
8.
dit Durell SE 《Biological reviews of the Cambridge Philosophical Society》2000,75(4):503-518
Individual feeding specialisation in shorebirds is reviewed, and the possilble mechanisms involved in such specialisations. Any specialisation can he seen as an individual strategy, and the optimum strategy for any given individual will be conditional upon its specific priorities and constraints. Some specialisations are related to social status and some to individual skills. Some are also probably frequency-dependent. However, most shorebird specialisations are constrained to a large extent by individual morphology, particularly bill morphology. For example, larger birds are able to handle larger prey, and birds with longer bills are able to feed on more deeply buried prey. Sex differences in bill length are uncommon in the Charardriidae, which are surface peckers, but are common in the Scolopacidae, which feed by probing in soft substrates. Sex differences in bill morphology are frequently associated with sex differences in feeding specialisation. There is evidence that different feeding specialisations are associated with different payoffs, in which case the probability of failing to reproduce or of dying will not be distributed equally throughout the population. I consider the population consequences of such feeding specialisations, particularly the different risks and benefits associated with different habitats or diets. I also consider the way in which individuals may differ in their response to habitat loss or change. I suggest that population models designed to predict the effect of habitat loss or change on shorebirds should have the ability to investigate the differential response of certain sections of the population, particularly different ages or sexes, that specialise in different diets or feeding methods. 相似文献
9.
High-level expression of the Endo-beta-N-acetylglucosaminidase F2 gene in E.coli: one step purification to homogeneity 总被引:1,自引:0,他引:1
The Endo F2gene was overexpressed in E.coli as a fusion protein joined to
the maltose-binding protein. MBP-Endo F2was found in a highly enriched
state as insoluble, inactive inclusion bodies. Extraction of the inclusion
bodies with 20% acetic acid followed by exhaustive dialysis rendered the
fusion protein active and soluble. MBP-Endo F2was digested with Factor
Xaand purified on Q-Sepharose. The enzyme was homogeneous by SDS-PAGE, and
appeared as a single symmetrical peak on HPLC. Analysis of the
amino-terminus demonstrated conclusively that recombinant Endo F2was
homogeneous and identical to the native enzyme.
相似文献
10.