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.
SYNOPSIS. Tetrahymena pyriformis syngen 1, mating type II, (optimal growth temperature ∼ 37 C) ordinarily dies out in 5-14 days at 0-5 C. Dying cells were lumpy, suggesting membrane damage. By supplying crude soy lecithin, survival at 0-5 C was prolonged (after growth in peptone-yeast-dextrin) to at least 22 weeks. Crude soy sterols or sitosterol or stigmasterol, and antioxidant, e.g., Ionox 330 or ascorbylpalmitate, permitted survival of cells in suspension or in growth media for at least 16-22 weeks. These sterols are known to protect against triparanol toxicity, which suggested that triparanol, which blocks cholesterol synthesis in higher animals, might enhance cold-induced injury. Triparanol was more toxic at 0–5 than at 28 C for cell suspensions and cells in growth medium; this toxicity was annulled by crude soy lecithin or β-sitosterol, the only phytosterol tested. The synthetic medium intended as a control on the crude media became toxic at 0–5 C. Protection against cold damage is discussed as a means of elucidating the role of sterols—especially phytosterols—and other lipids in maintaining the integrity of the ciliate cell membrane. 相似文献