Different Degrees Of Affinity Research Articles

Role of sediment composition in trace metal distribution in lake sediments

Sediment cores were collected from 20 lakes from the Muskoka region of Ontario, Canada, to study vertical changes in trace metal concentrations with depth and the distribution of metals amongst humic material, amorphous and crystalline Fe and Mn oxides, insoluble organics/sulphides, and silicates. Based on their total concentrations, trace elements displayed different degrees of affinity for the organic fraction (represented by organic C) and the mineral fraction (represented by Al). Certain elements (Hg, As, Sb, Pb, Cd, and Zn) displayed a positive correlation with organic C, a negative correlation with Al, and enrichment in surface sediments (with enrichment factors ranging from 2 to 24). Detailed speciation studies revealed that these elements were associated mainly with humic material and to a lesser extent with oxides in surface sediments. Other elements (Al, Cr, Co, Fe, and Mn) displayed a negative correlation with organic C, a positive correlation with Al, and no consistent enrichment in their total concentration at the surface. The speciation study revealed that metals of the latter group were mainly associated with the silicate fraction in both surface and deep sediments. This study shows that relative affinities for organic and mineral fractions play an important role in the distribution of trace metals during burial and diagenesis, and hence in the shape of their vertical profiles.

Synthesis and biological activity of a new series of N6-arylcarbamoyl, 2-(Ar)alkynyl-N6-arylcarbamoyl, and N6-carboxamido derivatives of adenosine-5'-N-ethyluronamide as A1 and A3 adenosine receptor agonists.

A new series of 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-beta-D-ribofuranuronamide++ +-b earing N-arylureas or N-arylcarboxamido groups at the purine 6 position and N-arylureas combined with halogens or alkynyl chains at the 2 position have been synthesized and tested for affinity at A1 and A2A adenosine receptors in rat brain membranes and at cloned rat A3 receptors expressed in CHO cells. The derivatives contained the 5' substituent found in the potent, nonselective agonist 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-beta-D-ribofuranuronamide++ + (NECA). While the carboxamido derivatives (9-13) showed affinity for A1 receptors, the urea derivatives (30-45) showed different degrees of affinity and selectivity for the A3 adenosine receptor subtype. In particular the derivative bearing a p-sulfonamidophenyl-urea at the 6 position, 31 showed a high affinity (Ki = 9 nM) and selectivity for the A3 receptors compared to that of the reference compound 1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-methyl-be ta-D-ribofuranuronamide (IB-MECA). Furthermore, the importance of the stereochemistry in the interaction of these ligands at the rat A3 adenosine receptors has been evaluated by introducing a chiral chain at the 6 position. The introduction of halogens or alkynyl chains at the purine 2 position of selected ureas did not give the expected enhancement of potency at A2A and/or A3 receptors but rather showed a dramatic reduction of A2A affinity, resulting in compounds with good A2A/A3 selectivity. For example, the 2-(3-hydroxy-3-phenyl-1-propyn-1-yl)-6-(4-methoxyphenylurea) derivative 61 showed the capability to bind simultaneously to A1 and A3 receptor subtypes, excluding the A2A receptor. Compound 31 was shown to be an agonist, 9-fold more potent than NECA, at A3 receptors in rat RBL-2H3 mast cell membranes through stimulation of binding of [35S]GTP-gamma-S.

Identification of stable plant cystatin/nematode proteinase complexes using mildly denaturing gelatin/polyacrylamide gel electrophoresis.

The biochemical interactions between two cystatins from rice seeds, oryzacystatin I (OCI) and oryzacystatin II (OCII), and the cysteine proteinases from three plant parasitic nematodes, Meloidogyne hapla, M. incognita and M. javanica, were assessed using standard protease assays and mildly denaturing gelatin/polyacrylamide gel electrophoresis (gelatin/PAGE). Activity detected in extracts of preparasitic second-stage larvae (J2) from M. hapla was optimal at pH 5.5 and was inhibited in vitro by the cysteine proteinase inhibitors trans-epoxysuccinyl-L-leucylamido-(4-guanidino) butane, hen egg cystatin, OCI, and OCII. As demonstrated by class-specific activity staining, all the activity measured between pH 3.5 and pH 7.5 was accounted for by a major proteinase form, Mhp1, and two minor forms, Mhp2 and Mhp3. Mhps were also detected in extracts and excretions of parasitic J2 and adult females, indicating their continuous expression throughout development of M. hapla, and their possible involvement in the extracellular degradation of proteins. Interestingly, the two plant cysteine proteinase inhibitors OCI and OCII showed different degrees of affinity for the major proteinase form, Mhp1. Both inhibitors almost completely inactivated this proteinase in native conditions but, unlike OCII, OCI conserved a high affinity for Mhp1 during mildly denaturing gelatin/PAGE, showing the differential stabilities of the OCI/Mhp1 and OCII/Mhp1 complexes. In contrast to Mhp1, the major cysteine proteinases detected in the two closely related species M. incognita and M. javanica were strongly inhibited by OCII, while the inhibition of OCI was partly prevented during electrophoresis. This species-related efficiency of plant cystatins against nematode cysteine proteinases could have practical implications when planning their use to control nematodes of the genus Meloidogyne.

Photosystem II Core Phosphorylation Heterogeneity, Differential Herbicide Binding, and Regulation of Electron Transfer in Photosystem II Preparations from Spinach

The effect of photosystem II core phosphorylation on the secondary quinone acceptor of photosystem II (Q(B)) domain environment was analyzed by comparative herbicide-binding studies with photosystem II preparations from spinach (Spinacia oleracea L.). It was found that phosphorylation reduces the binding affinity for most photosynthetic herbicides. The binding of synthetic quinones and of the electron acceptor 2,6-dichlorophenolindophenol is also reduced by photosystem II phosphorylation. Four photosystem II core populations isolated from membranes showed different extents of phosphorylation as well as different degrees of affinity for photosynthetic herbicides. These findings support the idea that heterogeneity of photosystem II observed in vivo could be, in part, due to phosphorylation.

Fc receptors on the surface of Toxoplasma gondii trophozoites: a confounding factor in testing for anti-Toxoplasma antibodies by indirect immunofluorescence.

Negative sera often produce false-positive polar patterns of fluorescence in indirect immunofluorescence tests for serum anti-Toxoplasma gondii antibodies, representing a confounding factor in the diagnosis of toxoplasmosis. In this work, we studied whether T. gondii trophozoites, the antigenic material used in the immunofluorescence tests, expressed surface Fc receptors that could cause the binding of normal immunoglobulins, thus producing false-positive results. We report here that T. gondii trophozoites indeed have Fc receptors on their surface. This was shown by the direct binding of purified human Fc to the parasite, evidenced by the subsequent binding of fluorescein-labeled Fab specific for human Fc. In addition, pretreatment of the parasite with excess purified Fc to saturate the surface Fc-binding sites abrogated the formation of polar fluorescence. The trophozoites appeared to express Fc receptors with different degrees of affinity for the specific ligand, since a diffuse fluorescence pattern was observed following incubation with 1 mg of Fc per ml (10 micrograms per well), whereas with 0.2 mg (0.2 micrograms per well), a majority of parasites showed polar fluorescence. This observation suggests that the Fc receptors accumulated at the polar cap are those with higher affinity. The present findings raise intriguing questions regarding the possible biological role(s) of the Fc receptors on T. gondii but, more immediately, indicated that pretreatment of the antigenic material with Fc, a commercially available reagent, constitutes a practical, simple way to avoid false-positive immunofluorescence test results due to the binding of nonspecific immunoglobulin to the parasite.

Vasopressin receptors from cultured mesangial cells resemble V1a type.

Mesangial cells respond to vasopressin by contraction and increased prostaglandin production. The purpose of the present study is to characterize vasopressin receptors from these cells. Glomeruli were isolated from rat kidneys and plated for explant growth of mesangial cells. Membranes were prepared from cells grown for 6 wk and tested for their ability to bind [3H]vasopressin (lysine vasopressin). These membranes contained a single class of specific vasopressin binding sites [equilibrium dissociation constant (Kd) = 10 +/- 1 nM, maximal binding capacity (Bmax) = 270 +/- 7 fmol/mg protein for 5 determinations]. Vasopressin induced a dose-dependent (apparent Kact value = 2 nM) accumulation of labeled inositol phosphates in myo[3H]inositol-prelabeled mesangial cells incubated in the presence of 10 mM of Li. Conversely, vasopressin failed to alter the adenylate cyclase activity of mesangial cell membranes. Competition experiments with a series of vasopressin structural analogues that have different degrees of affinity for V2-(renal), V1a- (vascular and hepatic), and V1b- (adenohypophyseal) receptors, indicated that vasopressin receptors from rat glomerular mesangial cells resemble the V1a- receptor subtype.

Purification and properties of extracellular xylan hydrolases of Streptomyces exfoliatus.

Fractionation of extracellular xylan hydrolases of a strain of Streptomyces exfoliatus MC1 (by salting out, molecular sieving and ion exchange chromatography) revealed the presence of five species of the enzyme. Three major fractions could be purified to homogeneity; two were apparently endohydrolases and the third an exo-xylan hydrolase. The three fractions showed different degrees of affinity to the substrate and differed considerably in their substrate specificities. One of the endo-enzymes was specific to xylan while the other could also attack cellulose, inulin and pectin. The exo-enzyme showed xylanolytic and cellulolytic functions only. The three fractions further differed in their response to the presence of metal ions, mercapto reagents and compounds. Although the pH and temperature optima were different, the three fractions functioned synergistically in the hydrolysis of xylan.

Comparative evaluation of the influence of some tetracyclines on chick embryo

To test the hypothesis that the tropism of tetracyclines for bone tissue is largely dependent on their affinity for calcium, a comparative study of the effects of 4 tetracyclines on the skeletal development of the chick embryo was performed. These were tetracycline, oxytetracycline, methacycline and doxycycline, possessing different degrees of affinity for divalent ions. Tetracycline, which has the highest degree of affinity for calcium, induced an appreciable reduction in skeletal development when injected into the yolk sac on day 4 of incubation. This reduction was less significant with equimolecular doses of oxytetracycline and methacycline, and even less with doxycycline, which among these 4 antibiotics has the lowest degree of affinity for calcium.