A new measure of cooperativity in protein-ligand binding

An allosteric binding system consisting of a single ligand and a nondissociating macromolecule having multiple binding sites can be represented by a binding polynomial. Various properties of the binding process can be obtained by analyzing the coefficients of the binding polynomial and such functions as the binding curve and the Hill plot. The Hill plot has an asymptote of unit slope at each end and the departure of the slope from unity at any point can be used to measure the effective interaction free energy at that point. Of particular interest in detecting and measuring cooperativity are extrema of the Hill slope and its value at the half-saturation point. If the binding polynomial is symmetric, then there is an extremum of the Hill slope at the half-saturation point. This value, the Hill coefficient, is a convenient measure of cooperativity. The purpose of this paper is to express the Hill coefficient for symmetric binding polynomials in terms of the roots of the polynomial and to give an interpretation of cooperativity in terms of the geometric pattern of the roots in the complex plane. This interpretation is then applied to the binding polynomials for the MWC (Monod-Wyman-Changeux) and KNF (Koshland-Nemethy-Filmer) models.     

Recovery of loss in chlorophyll and 2,6-dichlorophenol indophenol Hill reaction of isolated chloroplasts during dark induced aging of intact maize seedlings

Loss in the content of pigments and decline in the efficiency of thylakoid membranes to reduce 2,6-dichlorophenol indophenol (DCPIP) have been investigated during dark induced senescence of attached leaves of maize seedlings. The chlorophyll degradation during senescence is differentially inhibited by indoleacetic acid (IAA), gibberellic acid (GA) and kinetin. IAA and GA behave as mild senescence inhibitors in comparison to kinetin. However, in comparison to light, kinetin is relatively less efficient in counteracting senescence. Dark-induced loss in chlorophyll content is fully recovered by light when the dark incubation period is relatively short. The pattern of light recovery of loss in photoelectron transport during dark-aging is similar to the recovery kinetics of chlorophyll. Continuous kinetin treatment of dark-incubated seedlings inhibits the chlorophyll degradation but with decreased duration of kinetin treatment, the efficiency of the hormone to inhibit chlorophyll loss is reduced. The kinetin-induced inhibition of pigment loss is small in comparison with the effect of light.     

Quantitative evaluation of predation by spiders on the green rice leafhopper,Nephotettix cincticeps Uhler,by a sight-count method

A sight-count method for evaluation of predation by spiders on the green rice leafhopper, Nephotettix cincticeps was proposed and its applicability was tested under natural conditions. The number (n) of leafhoppers preyed on by spiders per rice hill per day was estimated by the formula: (1) where F is the frequency of predation observed per hill:P is given by dividing the time spent feeding on prey by 24 hours; and C refers to the total amount of feeding activity expressed in terms of the activity during the standard time interval. The total number (N) of prey attacked during the specified period can be given as follows: (2) With this method, the role of paddy-inhabiting spiders, Lycosa pseudoannulata, Oedothorax insecticeps, Tetragnatha spp, and Enoplognatha japonica, as predator of N. cincticeps was evaluated with reference to life tables of the prey. The advantages and limitation of the sight-count method were discussed as compared with other methods so far proposed.     

Isolation of polypeptides containing the intermolecular cross-link , '-dihydroxylysinonorleucine from dentin collagen

Insoluble dentin collagen was reduced with sodium borotritiide and then sequentially cleaved with cyanogen bromide and trypsin. Separation and purification of the labeled peptides were accomplished by gel filtration and ion-exchange chromatography. Two peptides were obtained containing 38 and 26 residues each, respectively. Both contained stoichiometric amounts of the collagen intermolecular cross-link δ,δ′-dihydroxylysinonorleucine. Their compositions are reported. The data indicate that one of the branches on each of the H-shaped peptides might be identical and the other branch on each is derived from different loci on the collagen molecule. Neither crosslink peptide involves the N-terminal portion of collagen.     

Energy-dependent endocytosis in erythrocyte ghosts. 3. Hydrophobic character of maleimide inactivation sites of ATPase and of endocytosis

The effects of a variety of reactive compounds on endocytosis in erythrocyte ghosts were observed. Of these reagents, only alkylating reagents were effective at low concentrations. This suggested that an alkylatable site, probably a sulfhydryl group, was important in endocytosis. In a series of N -substituted maleimides, effectiveness of the alkylating agent in inactivating both ATPase and endocytosis correlated very well with a high value of the partition coefficient between octanol and water. This suggested that a hydrophobic region was present at the site of inactivation, so that strongly hydrophobic alkylating agents were bound more firmly by this site. The action of the N -substituted maleimides was clearly due to the reactivity of the carbon-carbon double bond in the heterocyclic ring, since saturation of this bond completely destroyed the effectiveness of the inhibitor. Statistical analysis of the dependence of the effectiveness of N-substituted maleimides upon partition coefficient and Hammett sigma parameters showed that the partition coefficient was by far the most important factor which controlled the effectiveness of these inhibitors. The sigma parameter played a lesser role. The dependence of the effectiveness of the maleimides on these two parameters was the same, within the statistical error, for both the ATPase activity and endocytosis activity. This suggested that inhibition of endocytosis was due to reaction with the same site responsible for inhibition of ATPase.     

Influence of interferon on human monocyte to macrophage development

The effect of interferon-α (Wellferon) on human monocyte to macrophage maturation in vitro has been investigated. Cell volume and three markers, acid phosphatase, leucine aminopeptidase, and phagocytosis, which increase with maturation, have been studied employing recently developed flow cytofluorometric techniques. The increase in cell volume and in the expression of all three markers was inhibited in a dose-dependent manner in monocyte cultures given 50–300 U/ml of interferon within 2 hr of culture initiation. An initial dose of 300 U/ml of interferon, removed from the cultures after 24 hr, was as effective in inhibiting the development of each of the markers as three 100 U pulses on three consecutive days, and as effective as 300 U interferon left in throughout the culture period. Histogram analysis of marker expression indicated that all monocytes, and not a subpopulation, were affected by the interferon. Cytotoxic activity of freshly isolated monocytes rapidly decayed when the cells were cultured under standard maturation conditions. The addition of interferon to the cultures prevented the loss of this activity while also preventing the development of more mature cells. It appears that maintenance of the cytotoxic state is one influence of interferons; however, it may be that these cells have also been directed toward alternate pathways of macrophage differentiation.     

Clonidine reduces elevated cerebrospinal fluid catecholamine levels in patients with essential hypertension

Cerebrospinal fluid (CSF) catecholamines were measured in normotensive patients and in patients with mild to moderate essential hypertension. CSF-norepinephrine (NE) concentrations were 50% lower in the normotensive individuals (127 ± 28 vs. 240 ± 23 pg/m1) (P<0.01). In hypertensive patients, CSF-NE was inversely related to age (r =-0.68; P<0.01) and directly related to plasma NE (r = 0.61; P<0.05). Clonidine (450 mcg/day for 2 weeks) significantly reduced CSF-NE (?40%) in hypertensive patients. In addition, it decreased blood pressure, plasma and urinary NE. Urinary VMA was not affected by clonidine. No correlation was observed between clonidine effects on BP and on plasma or CSF catecholamines. This study indicates that patients with essential hypertension have elevated levels of CSF-NE which are reduced after treatment with clonidine. The elevation of CSF-NE suggests that central (spinal?) noradrenergic activity may be increased in patients with mild to moderate essential hypertension, and that can be reduced by treatment with clonidine.     

Differential changes in the electron transport properties of thylakoid membranes during aging of attached and detached leaves, and of isolated chloroplasts

Abstract. Aging of chloroplasts both in vivo and in vitro causes a considerable loss in the 2,6-dichlorophenol indophenol (DCPIP)-Hill reaction with water as electron donor. The loss can be reduced by exogenous electron donors like diphenyl carbazide (DPC). suggestive of aging-induced damage of the oxygen evolving system. Aging also brings about a considerable loss in methylviologen (MV) reduction mediated by Photosystem I (PS I) of chloroplasts with an ascorbate-DCPIP couple as the electron donating system.
The loss in the electron transport ability of the plastids is faster during in vitro compared to in vivo aging of the chloroplasts.
Light protects the photo-electron transport ability of chloroplasts during aging of intact leaves in contrast to its action during aging of the isolated organelles.     

Stopover ecology of Red-flanked Bush Robin (Tarsiger cyanurus) at Maoershan, Northeast China

The conservation of migratory songbirds in China faces challenges similar to those in other parts of the world such as Europe and North America. Migratory songbirds have a complex life history and are associated with large spatial scale. Events that occur during migration play a vital role in determining population status. Little is known about the stopover behavior of migratory songbirds in China during their passage, including stopover duration, energetic condition (e.g., the amount of fat stores), and the habitat of these birds. We investigated migration timing, stopover duration, change of energetic condition and sex-related variations among Red-flanked Bush Robins (Tarsiger cyanurus) at a stopover site in Northeast China. A total of 1 751 Red-flanked Bush Robins were captured in the fall of 2002, with further 684 captured in the spring of 2003. The body mass of the fall birds was higher than that of the spring ones. The condition index (i.e., body mass adjusted for body size) was lowest among spring females. Birds were more likely to stay longer in fall than in spring. We detected a positive relationship between the time of initial capture and condition index regardless of season or sex, suggesting that the birds were able to replenish energy stores. The net daily mass gain was the highest among males in the fall (3% of body mass). The net daily mass gain would sustain a flight of 0.6 hours for females and 3.1 hours for males in the fall. The stopover biology of Red-flanked Bush Robins is similar to that of some migratory songbirds in Europe and North America. For example, the spring passage time and fat store variation between the sexes concurs with the hypothesis that males are selected to arrive at their breeding grounds as early as food resources or climatic conditions are adequate in the spring. Further research on stopover ecology is urgently required in China to achieve a better understanding of migratory behavior and ensure the conservation of these migratory songbirds.     

抑制剂K-23对菠菜光系统Ⅱ放氧活性和希尔反应的影响

研究了新的抑制剂K-23对波菜(Spinacia oleracea Mill.) PSⅡ放氧活性和2,6-dichlorophenol indophenol(DCIP)光还原活性的影响.研究发现:抑制剂K-23在低浓度时对PSⅡ放氧活性有明显促进作用,而对DCIP光还原活性的促进作用不太明显.在高浓度时抑制PSⅡ放氧活性和DCIP光还原.对K-23的抑制部位进行了初步探讨.