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21.
The substrate specificity of phospholipid/Ca2+-dependent protein kinase (protein kinase C) was studied using synthetic peptides, in particular those corresponding to the amino acid sequence around serine 115 in bovine myelin basic protein (MBP). It was found that MBP (104-118) and MBP (104-123) were substrates for the enzyme, with apparent Km values of 14 and 10 microM, respectively. Neither MBP (111-118) nor MBP (111-123) were phosphorylated, indicating that an additional segment of sequence extending toward the N terminus, but not toward the C terminus, was essential for the substrate activity of the peptides. Of the alanine-substituted analogs examined, [Ala 105] MBP (104-118) was comparable to the parent peptide, whereas [Ala 107] MBP (104-118) and [Ala 113] MBP-(104-118) were much poorer substrates. These findings indicated that lysine 105 was not essential, but both arginine 107 and arginine 113 were important specificity determinants. Initial studies revealed that [Ala 113] MBP (104-118) inhibited phosphorylation by the enzyme of the parent peptide and, to a lesser extent, the intact MBP(1-170). Serine 115 was the only site phosphorylated in the analog peptides [Ala 105] MBP (104-118) and [Ala 107]MBP (104-118). In the parent peptide, serine 115 was the initial site of phosphorylation but after prolonged phosphorylation other sites became phosphorylated (serine 110 and/or serine 112), further supporting the concept that arginine residues act as essential substrate specificity determinants for phospholipid/Ca2+-dependent protein kinase. 相似文献
22.
Development of flower buds in thin-layer cultures of floral stalk tissue from tobacco: Role of hormones in different stages 总被引:4,自引:0,他引:4
The in vitro development of flower buds was studied on tissue explants of epidermis and subepidermal cortex from the flower stalks of Nicotiana tabacum L. cv. Samsun. The number of flower buds formed depended mainly on cytokinin concentration. Auxin acted as a modifier in a complex way. In early development, NAA at 1 μ M decreased the number of buds initiated and delayed bud emergence. At a later stage, auxin promoted bud outgrowth at the same concentration. Optimal results were obtained when explants were first incubated at low auxin concentration for 3–5 days and subsequently transferred to an elevated auxin level. Physiological processes that lead to flower bud initiation start very soon after the onset of incubation. This was inferred from experiments whereby explants were first cultured at an inductive cytokinin concentration and then transferred to a non-inductive hormone level. 相似文献
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K O Ash J B Smith J W Kemp M B Lynch F G Moody J L Raymond M R McKnight R R Williams 《Clinical physiology and biochemistry》1983,1(6):293-299
Ouabain binding to erythrocyte membranes is increased in obese subjects. Three study groups are compared: 14 reference subjects, 102 +/- 16% of ideal weight; 9 obese on unrestricted diets, 207 +/- 16% of ideal weight; 11 obese on restricted diets, 202 +/- 35% of ideal weight. A reproducible (CV = 11.3%) ouabain-binding assay is used to measure Na+-K+ ATPase sites in erythrocyte membranes. The number of binding sites per red blood cell for obese subjects on unrestricted diets, 431 +/- 30, is greater than for the reference group, 346 +/- 66 (p less than 0.01), or for obese subjects on restricted diets, 371 +/- 68 (p less than 0.05). These data suggest that caloric intake influences the number of Na+-K+ ATPase sites. Scatchard plots indicate only one type of binding site for ouabain with an affinity constant of about 3 X 10(8) M-1. 相似文献
26.
Lectin- and ionophore-stimulated Ca2+ influx in murine lymphocytes: inhibition by disialoganglioside 总被引:1,自引:0,他引:1
Gangliosides suppress lymphocyte mitogenesis when added exogenously to the cells. On the premise that the mechanism of ganglioside action may be an interference with primary induction events, mitogen-induced 45Ca2+ influx in murine lymphocytes was studied. Disialoganglioside (GD1a) at physiopathological concentrations inhibits concanavalin A-induced 45Ca2+ uptake as well as blast transformation. The suppressive action of GD1a is both concentration dependent (50% suppression at 13 microM) and very rapid (within 1 min). GD1a is not cytotoxic nor does it significantly alter the rate of Ca2+ efflux. The uptake studies were extended to A23187, a compound with mitogenic and specific divalent cation ionophore activities. Ca2+ uptake by lymphoid cells from AKR/J, Swiss, and CBA mice is stimulated by A23187; and GD1a, in a dose-dependent manner, inhibits the ionophore-induced 45Ca2+ influx. Pretreatment of thymocytes with GD1a renders the cells greatly insensitive to the subsequent ionophore activity of A23187. The results suggest that exogenous gangliosides may function as an inhibitor of some of the mitogen-triggered early events, including Ca2+ metabolism, and thus influence the immunological behavior of intact lymphoid cells. 相似文献
27.
Highly purified feather keratin mRNA, prepared by dissociation of mRNP particles in Na dodecyl sulphate, was translated in a wheat embryo cell-free system with similar efficiency to rabbit globin mRNA and RNA purified from cucumber mosaic virus. The only detectable products of translation of the keratin mRNA were keratin chains, which were identical to native keratin chains as judged by several different criteria. These results support previous conclusions that the keratin mRNA can be obtained in a pure state. 相似文献
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Hexose phosphate synthetase from Methylococcus capsulatus makes d-arabino-3-hexulose phosphate 总被引:2,自引:0,他引:2 下载免费PDF全文
M. B. Kemp 《The Biochemical journal》1974,139(1):129-134
The product of the reaction catalysed by hexose phosphate synthase prepared from Methylococcus capsulatus was dephosphorylated and the sugar moiety purified. The sugar and derivatives were compared by various chromatographic and other methods with authentic samples of allulose (psicose), d-erythro-l-glycero-3-hexulose and d-erythro-d-glycero-3-hexulose. The sugar is not allulose, as was previously thought on the basis of less extensive evidence (Kemp & Quayle, 1966), but is in fact d-erythro-l-glycero-3-hexulose (d-arabino-3-hexulose). This identification is consistent with recent studies which have shown that hexose phosphate synthase catalyses the condensation of formaldehyde with d-ribulose 5-phosphate rather than with d-ribose 5-phosphate (Kemp, 1972). 相似文献
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