Equilibrium dialysis results are presented for Ca(II) and Mg(II) ion binding to human and bovine prothrombin and fragment 1. Ca(II) ions bind cooperatively, Mg(II) does not. 相似文献
A novel class of mutations affecting the developmental expression of SerH cell surface antigen genes of Tetrahymena thermophila is described. Unlike previous categories of mutation, the four independently isolated mutations of this class act through the cytoplasm to affect SerH genes during macronuclear development. That is, macronuclei which develop under the influence of mutant cytoplasm do not subsequently express H, most likely because the developmental processing of SerH genes is affected. The cytoplasmic effect is specific for the SerH locus and is independent of which SerH allele is present. In place of H, hitherto unknown antigens are expressed. Expression of SerH can be rescued during development either by wild-type cytoplasm exchanged between conjugants or by the homozygous wild-type genotype. The mutations segregate independently of the SerH genes and identify one, possibly two, bistable genes. Possible models to explain these results are discussed. 相似文献
Methods used to estimate the (nonosmotic) bound water fraction (BWF) (i.e. apoplast water) of spinach (Spinacia oleracea L.) leaves were evaluated. Studies using three different methods of pressure/volume (P/V) curve construction all resulted in a similar calculation of BWF; approximately 40%. The theoretically derived BWF, and the water potential (Ψw)/relative water content relationship established from P/V curves were used to establish the relationship between protoplast (i.e. symplast) volume and Ψw. Another method of establishing the protoplast volume/Ψw relationship in spinach leaves was compared with the results from P/V curve experiments. This second technique involved the vacuum infiltration of solutions at a range of osmotic potentials into discs cut from spinach leaves. These solutions contained radioactively labeled H2O and sorbitol. This dual label infiltration technique allowed for simultaneous measurement of the total and apoplast volumes in leaf tissue; the difference yielded the protoplast volume. The dual label infiltration experiments and the P/V curve constructions both showed that below −1 megapascals, protoplast volume decreases sharply with decreasing water potential; with 50% reduction in protoplast volume occurring at −1.8 megapascals leaf water potential. 相似文献
Greenhouse and field experiments were performed to determine if increased leaf resistance induced by exogenous application of abscisic acid (ABA) could enhance the water status of transplanted bell pepper seedlings. Seedling survival and yield were also monitored in the field experiment. When seedlings were transplanted into either wet or dry potting mix in the greenhouse, ABA increased leaf resistance and leaf water potential. In the field, plots were irrigated either immediately after, or 1 day after transplanting. Under both treatments, ABA application resulted in increased leaf resistance and water potential, but seedling survival and yield were enhanced due to ABA only in plots which were irrigated 1 day after transplanting. It is concluded that antitranspirant application can reduce transplant shock and increase yield of bell pepper. 相似文献
Chemical modification of the gamma-carboxyglutamyl (Gla) residues of bovine prothrombin fragment 1 using the formaldehyde-morpholine method in the presence of 100 Kappm Tb3+ ions at pH 5.0 provided a modified protein containing 3 gamma-methyleneglutamyl residues (gamma-MGlu) and 7 Gla residues (bovine 3-gamma-MGlu-fragment 1). The modified protein bound the same number of Ca2+ ions as the native protein (six to seven), exhibited 28Mg2+-binding properties identical to native fragment 1 (five Mg2+ ions bound), exhibited the metal ion-promoted quenching of the intrinsic fluorescence in a manner similar to the native protein, but did not bind to phosphatidylserine (PS)/phosphatidylcholine (PC) vesicles in the presence of Ca2+ ions. Modification of the bovine protein using [14C]formaldehyde-morpholine provided a 14C-labeled 3-gamma-MGlu-fragment 1 suitable for sequence analysis. Edman sequencing of the peptides released by a tryptic digest of the reduced and carboxymethylated bovine [14C]3-gamma-MGlu-fragment 1 indicated that Gla residues at positions 7, 8, and 33 had been converted to [14C]gamma-methyleneglutamyl residues. In addition Lys97 was found to contain a 14C label. Similar analysis of the human [14C]3-gamma-MGlu-fragment 1 indicated that Gla residues at positions 7 and 32 were major modification sites and that Gla residues at positions 6 and 14 were partially modified. Lysine 96 was also modified in the human protein. The incorporation of a 14C label at Lys97 in bovine 3-gamma-MGlu-fragment 1 protein is not responsible for the loss of Ca2+-promoted binding to PS/PC vesicles. We suggest that Gla residues 7, 8, and 33 are elements of the first Ca2+-binding site; occupancy of this site establishes the Ca2+-specific conformation which is essential for the Ca2+-promoted interaction of the bovine protein with PS/PC vesicles. These studies also suggest that the loss of Gla residues at positions 7 and 32 prevents the formation of the initial Ca2+-binding site in the human protein. 相似文献
Experiments were undertaken with field-grown potato (Solanum tuberosum L.) plants to test the hypothesis that altering leaf:tuber water potential gradients within a plant subjected to low soil moisture will allow greater Ca accumulation in tubers and reverse Ca deficiency-related tuber necrosis. Antitranspirant formulations containing a wax emulsion and a spreader/sticker surfactant increased leaf water potential during a drought episode, significantly reducing the potential gradient that develops between leaf and tuber during a period of stress. Increased leaf water potential in treated plants was associated with decreased leaf Ca and increased tuber Ca. Tuber necrosis was found to be reduced in treated plants, thus increasing tuber quality. 相似文献
It is controversial whether dopamine (DA) is a peripheral neurotransmitter in the cardiovascular/renal system. The endogenous concentration of DA in the heart and blood vessels is generally only a fraction (5%) of that of norepinephrine (NE). With perhaps the exception of the kidney, the majority of the evidence suggests a precursor role for this amine rather than that of a neurotransmitter. The main weakness of arguments favoring DA as a vascular neurotransmitter is relative lack of data showing selective DA release and lack of effects of selective DA antagonists on neural stimulation. However, DA receptors have been characterized in cardiovascular tissues and are of two types: DA1 receptors located on vascular smooth muscle (postjunctional), which appear to mediate relaxation of the muscle, and DA2 receptors located on sympathetic nerves (pejunctional), which inhibit NE release. These receptors are interesting and potential target sites for novel cardiovascular drug action for the treatment of hypertension and renal ischemia. Moreover, selective DA receptor agonists will be important tools in understanding the role of DA receptors in normal and disease states. 相似文献
The effects of reduced reaction medium osmotic potential (0.67 molar sorbitol as compared to a control treatment with 0.33 molar sorbitol) on the enzymic steps of the photosynthetic carbon reduction cycle were investigated using isolated spinach (Spinacia oleracea L. var Longstanding Bloomsdale) chloroplasts. Reversal of reduced osmotic potential inhibition of photosynthetic rates by a stromal alkalating agent (NH4Cl) was associated with specific steps of the cycle. Low osmotic potential induced stromal acidification was found to be facilitated by osmotically induced chloroplast shrinkage. However, the action of the alkalating agent was found not to be associated with reversal of osmotically induced morphological changes of the stromal compartment.
Labeled metabolite analyses indicated that the osmotic stress treatment caused the substrate for fructose 1,6-bisphosphatase (FBPase) to build up in the absence of NH4Cl, and the substrate for phosphoribulokinase to increase in the presence of NH4Cl. These data were interpreted as indicating that the most severe effect of osmotic stress on photosynthesis is at the site of FBPase, and that this inhibition is mediated by osmotically induced stromal acidification. Phosphoribulokinase activity inhibition at the low osmotic potential treatment was apparently less severe and not mediated by stromal acidification. A third site of osmotic inhibition, which was reversed by NH4Cl, and therefore was assumed to be mediated by stromal acidification, was at the step of ribulose 1,5-bisphosphate carboxylase.
Additions of NH4Cl also enhanced the activity of the pH-insensitive phase of the photosynthetic carbon reduction cycle, 3-phosphoglyceric acid reduction, at the stress treatment. This effect was thought to be mediated by the removal of the block at FBPase. A model was proposed to outline the relative severity of osmotic stress effects at various sites of the photosynthetic carbon reduction cycle.