SUBSTANCE P has been synthesized by the solid-phase procedure of Merrifield1,2 according to the sequence H-Arg-Pro-LysPro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2 reported in the previous letter. 相似文献
The use of chromic chloride as a coupling reagent has made it possible to coat red cells with rhinovirus protein. This is shown by immunofluorescence, electron microscopy and immunocolloidal experiments. 相似文献
THE carboxy-terminal tetrapeptide of gastrin, Trp-Met-Asp-Phe-NH2, has the same biological activity as the parent hormone1. Morley2,3 showed that certain substitutions in the Trp, Met and Phe positions gave active analogues and concluded that these positions are concerned only with binding at the site of action. In contrast, the only substitution in aspartic acid that gave activity was tetrazolyl for the β-carboxyl, thereby maintaining a proton donor of similar size at this position. Morley concluded that the aspartyl residue has a functional rather than a binding role and presumably is indispensable. The carboxy-terminal octapeptide of cholecystokinin (OP-CCK) contains the carboxy-terminal tetrapeptide of gastrin and has gastrin-like activity4. We report here that the synthetic analogue of OP-CCK, in which alanyl is substituted for aspartyl at the position in question illustration, stimulates gastric acid secretion. In conscious cats with gastric fistulas5, dose-response curves were established for gastric acid response to OP-CCK, 7-Ala OP-CCK and pentagastrin6. The peptides were given by continuous intravenous infusion and response is taken as peak 10 min output during a 30 min infusion at each dose level (Fig. 1). Assigning a potency of 1 to OP-CCK the relative molar potency of 7-Ala OP-CCK is about 1/110 and of pentagastrin is about 1/4. We also tested the analogue of gastrin tetrapeptide in which alanyl is substituted for aspartyl illustration and found no detectable stimulation of acid secretion at doses as high as 15 mg/kg h, confirming similar negative findings by Morley2 in rat. This suggests that the weak action of alanyl substituted analogues cannot readily be detected without the enhancement of potency conferred by the sulphated tyrosyl of OP-CCK7. Ondetti et al.7 showed that 7-Ala OP-CCK contracts guinea-pig gallbladder with a potency about 1/150th that of OP-CCK, comparable with that reported here for acid secretion. This suggests that the same part or parts of the molecule are required for cholecystokinetic action and for gastric secretory action; the aspartyl residue in the penultimate position is dispensable for both of these actions. On the assumption that gastrin and CCK act at the same site8, we propose that the corresponding aspartyl residue of gastrin is similarly dispensable. For a direct test of this hypothesis, studies are needed of the synthetic analogue in which alanyl is substituted for the penultimate aspartyl in gastrin hepta-decapeptide, perferably gastrin II with sulphated tyrosyl because it is more potent than gastrin I in certain species9.
Extensive surveys of possible aphid habitats in South Australia indicated that irrigated perennial grass pastures in the Mount Lofty Ranges and Lower Murray Valley were summer refuges for Rhopalosiphum padi (L.) (Hemiptera: Aphididae). Large numbers of aphids build up in these pastures each year during autumn (April and May) with numbers peaking in May. The size of the May peak was related to the number of aphids surviving the summer. The proportions of alates were highest in May and August/September. Both peaks coincided with a photoperiod of between 11.2 and 11.5 h, and partial correlations suggested that aphid density, photoperiod and temperature were all significant determinants of alate production. 相似文献
The distribution of virus-infected cells was examined, by fluorescence microscopy, within plants of a range of potato clones infected with potato leafroll luteovirus (PLRV). This range included nine PLRV-resistant clones, of which four were transgenic lines carrying the PLRV coat protein gene and five were conventionally bred. Plants of these clones were resistant to PLRV multiplication and accumulated less virus antigen in leaf tissue than did susceptible clones. Indirect fluorescent antibody staining of thin sections from carbodiimide-fixed petiole tissue revealed that in plants of PLRV-susceptible clones, virus-infected cells were abundant within both external (abaxial) and internal (adaxial) phloem bundles. In plants of the PLRV-resistant conventionally bred clones and in resistant transgenic lines of cv. Pentland Squire, virus-infected cells were much fewer in number and largely restricted to internal phloem bundles. In resistant transgenic lines of cv. Désirée, this restricted distribution of PLRV antigen was only detected in petioles of young leaves. The results suggest that the transgenic and a host-mediated type of resistance that restricts virtis multiplication have underlying similarities. 相似文献
Nest site choice and nesting success were studied in the Mauritius Fody Foudia rubra, a rare, island-endemic bird. Most pairs whose nests were found nested only in exotic plantation trees (Cryptomeria, Eucalyptus and Pinus) although native trees were available; around half of the total population nested in exotics. Most nesting failure resulted from nest predation, apparently by exotic Black Rats Rattus rattus and Crab-eating Macaques Macaca fascicularis. Nesting success was much higher in Cryptomeria (46%) than in other tree species (6%), and I conclude that this fact explains why fodies selected Cryptomeria for nesting. The same seems certain to be true for the Pink Pigeon Columba mayeri, which nested only in Cryptomeria. Larger samples of nests might reveal that Pinus and Eucalyptus support a nesting success intermediate between native trees and Cryptomeria, thereby explaining their use for nesting. 相似文献
The red wattlebird, a large Australian honey eater, defends feeding territories from other nectar-feeding birds. One such territory decreased in size and experienced fewer intruders as the density of flowers increased. Daily energy production from the nectar in the territory closely approximated the energy requirements of the territory holder. The bird was probably minimizing energetic costs rather than maximizing energy intake. 相似文献
Three primary approaches have been used to study the geneticsof migration: the analyses of population differences, of singlelocus effects, and of polygenic influences. Studies of populationsreared under similar conditions in "common garden" experimentsfrequently reveal gene effects contributing to differences inmigratory tendency. Single locus effects are known, but arenot common, a result to be expected given that migration iscomplex. Quantitative genetic studies reveal that heritabilitiesfor migration related traits are often high (approximately 0.5or more) suggesting significant amounts of genetic variationon which natural selection can act. Analyses of genetic correlationsdemonstrate that migratory behavior is part of a syndrome thatincludes aspects of both physiology and life history traits.The latter are characteristically those which contribute tocolonizing ability. Migratory behavior thus does not evolvein isolation. New migration patterns are still evolving, aswould be predicted from observed environmental changes and thegenetic variation present in migratory species. 相似文献