Small-angle X-ray scattering studies of fibrin film: comparisons of fine and coarse films prepared with thrombin and ancrod

Measurements of small-angle x-ray scattering have been made on films prepared from fine and coarse (i.e., formed at high and low, respectively, pH and ionic strength) clots of bovine fibrin by osmotic shrinkage or compression in one dimension. Intensity profiles were obtained with pinhole geometry on films stretched up to a stretch ratio of 1.43. In unstretched coarse films, repeat spacings were seen at about 245, 120, and 77-80 A. These peaks can probably be identified with the first, second, and third orders of the well-known fibrin repeat of 225 A. In unstretched fine films, only the 77-80 A spacing was seen. In this case, the first two orders may be weak because the half-staggered arrangement of monomer units giving rise to the 225 A reflection is not reinforced by lateral aggregation of protofibrils; the third order may be strong since the molecular subdomains appear to divide the repeat roughly into thirds. After stretching, the 77-80 A spacing persisted in the meridional direction but almost disappeared in the equatorial. Experiments on unstretched films prepared with ancrod substituted for thrombin gave similar results.     

N-iodoacetyltyramine: preparation and use in 125I labeling by alkylation of sulfhydryl groups

Preparation and use of N-iodoacetyltyramine in generation of 125I-labeled compounds is described. The kinetics of alkylation of N-acetylcysteine by N-iodoacetyltyramine (k2 = 3.0 M-1 s-1) and N-chloroacetyltyramine (k2 = 0.12 M-1 s-1) indicate that N-iodoacetyltyramine is more useful for labeling sulfhydryl-containing compounds to high specific activity with 125I. Conditions for preparation of carrier-free 125I-labeled N-iodoacetyl-3-monoiodotyramine in 50% yield based on starting iodide are described. The high degree of group specificity of N-iodoacetyl-3-monoiodotyramine reaction with sulfhydryl groups is demonstrated by the high reactivity toward sulfhydryl-containing bovine serum albumin and low reactivity toward N-ethylmaleimide-blocked bovine serum albumin and IgG. 125I-labeled N-iodoacetyl-3-monoiodotyramine was also used to prepare an 125I-labeled ACTH derivative that retains full biological activity, further demonstrating the selectivity toward reactions with sulfhydryl groups.     

Manganese-binding proteins of the oxygen-evolving complex

The extrinsic 33-kDa protein (P33) was cross-linked covalently to the binding site on P33-depleted PSII preparations which is responsible for reconstitution of photosynthetic water oxidation after PSII preparations have been washed with 1 M CaCl2. Conditions were found in which more than half of the cross-linked protein complexes formed in the PSII preparations retained the ability to catalyze the oxidation of water. The complex is composed of the P33 cross-linked to the D1 and D2 proteins and a 34-kDa protein, which is present in lower abundance than the other three proteins. After solubilization of the membranes with SDS and purification by preparative SDS-PAGE, the complex retains bound manganese and can catalyze the conversion of H2O2 to O2. Calcium and chloride increased the catalase activity of the purified cross-linked complex while lanthanum or hydroxylamine abolished the activity. By use of the specific activity of the H2O2-dependent reaction to follow the extent of purification of the cross-linked complex, the most highly purified complex was determined to contain 0.34 microgram of manganese/180 micrograms of protein. The mole ratio of Mn/protein was calculated to range from 3.6 to 4.5 depending on the assumed stoichiometry of the protein subunits. The results presented here provide direct evidence that one or more of the three proteins that have cross-linked to the P33 are responsible for binding the manganese of the oxygen-evolving complex.     

Correction of the N-terminal sequences of the human plastin isoforms by using anchored polymerase chain reaction: identification of a potential calcium-binding domain.

Plastins are a family of at least three cytoplasmic protein isoforms that are expressed differentially between cells of the hematopoietic lineages and cells of solid tissues. Expression of the L-plastin isoform appears to be restricted to replicating blood cells, and the two T-plastin isoforms appear to be restricted to replicating cells of solid tissues. However, L-plastin is induced in many human solid tumor-derived cells. We used the anchored polymerase chain reaction technique to amplify and clone the missing 5' ends of plastin mRNAs. We found that both plastin isoforms contain a potential calcium binding site near the N terminus.     

Substitution of a proline for alanine 183 in the hinge region of phosphoglycerate kinase: Effects on catalysis, activation by sulfate, and thermal stability

A hinge-bending domain movement has been postulated as an important part of the catalytic mechanism of phosphoglycerate kinase (PGK) (Bankset al., 1979). In order to test the role of the flexibility of a putative interdomain hinge in the substrate- and sulfate-induced conformational transitions, alanine-183 was replaced by proline using site-directed mutagenesis. The maximal velocity of the Ala 183Pro mutant, measured at saturating concentrations of ATP and phosphoglycerate (5 mM and 10 mM, respectively) and in the absence of sulfate ions, is increased approximately 21% in comparison to the wild type PGK. TheK _m values for both substrates are essentially unchanged. The effect of sulfate on the specific activity of the Ala 183Pro mutant and the wild type PGK was measured in the presence of 1 mM ATP and 2 mM 3-phosphoglycerate (3-PG). A maximum activation of 70% was observed at 20 mM sulfate for the mutant enzyme, as compared to 130% activation at 30 mM sulfate for the wild type PGK. These results demonstrate that the increased rigidity of the putative hinge, introduced by the AlaPro mutation, does not impair catalytic efficiency of phosphoglycerate kinase, while it appears to decrease the sulfate-dependent activation. The differential scanning calorimetry (DSC) studies demonstrate an increased susceptibility of the Ala 183 Pro mutant to thermal denaturation. In contrast to one asymmetric transition observed in the DSC scan for the wild type PGK, withT _m near 54°C, two transitions are evident for the mutant enzyme withT _m values of about 45 and 54°C. Using a thermodynamic model for two interacting domains, a decrease in the free energy of domain-domain interactions of about 2 kcal was estimated from the DSC data.     

The arcB gene of Escherichia coli encodes a sensor-regulator protein for anaerobic repression of the arc modulon

The arcA (dye) and arcB genes of Escherichia coli are responsible for anaerobic repression of target operons and regulons of aerobic function (the arc modulon). The amino acid sequence of ArcA (Dye) indicated that it is the regulator protein of a two-component control system. Here we show that ArcB is a membrane sensor protein on the basis of its deduced amino acid sequence (778 residues), hydropathicity profile, and cellular distribution. On the carboxyl end of the ArcB sequence there is an additional domain showing homology with conserved regions of regulator proteins. Deletion into this domain destroyed ArcB function. ArcB conserved a histidine residue for autophosphorylation of the sensor proteins, and aspartic residues important for the regulator proteins.     

厦门附近海域浮游甲藻类的分布

本文报道了厦门附近海域浮游甲藻类49种,并对其生态特性以及与海洋环境因素的关系进行了详细研究与讨论。分析的204号样品,系1980年9月至1981年8月,逐月采自厦门海域的浔江区(Ⅰ区),西港区(Ⅱ区)和九龙江口区(Ⅱ区)。     

罗汉果组培苗的栽培研究

本文报道罗汉果组培苗的栽培研究结果,为罗汉果在生产上推广应用组培苗栽培,提供有效的技术措施。     

国产磨芋属的染色体核型报道(1)

本文报道了磨芋属(Amorphophallus Blume)六个种的染色体数目和核型,其中5个种属于首次报道。其核型公式如下: 1.滇磨芋 K(2n)=2x=26=26m.2.磨芋 K(2n)=2x=26=26m.3.攸落磨芋K(2n)=2x=26=22m(2SAT)+4sm.(2SAT).4.西盟磨芋 K(2n)=2x=26=20m+4sm+2st.5.勐海磨芋 K(2n)=2x=26=22m+4sm.6.白磨芋 K(2n)=2x=26=20m(2SAT)+6sm。