Improved Stability of Methanolic Wright's Stain with Additive Reagents

Additive reagents have been investigated to improve the stability of methanolic Wright's stain. The addition of ammonium halides, monoalkyiamine hydrochlorides, dialkylamine hydrochlorides or trialkylamine hydrochlorides to methanolic Wright's stain was found to enhance the stability of stain components in methanol. No change in performance is observed with these additives present. Random precipitation in the stain solution was still observed with the addition of ammonium halides and monoalkyiamine hydrochlorides. No precipitation was found in stain solutions containing hydrochlorides of most dialkylamines and trialkylamines. Of the compounds evaluated, 0.6% diethylamine hydrochloride added to methanolic stain solutions produced the most desirable overall results. Mechanisms of stabilization and precipitation in these stain solutions are proposed, Essentially, separation of the thiazine-eosinate ion pair through interaction with an appropriate additive increases stain stability. The solubilities of thiazine-eosinate or additive cation-eosinate ion pairs in methanol determine the formation of precipitate in such stain solutions.     

Towards a theory of the evolution of butterfly colour patterns under directional and disruptive selection

Two general models for the transspecific evolution of butterfly colour patterns are advanced: directional selection acting equally on both sexes, and disruptive selection involving periods of polymorphism. To consider possible outcomes of me latter process, a morphism notation based on an integrated classification for polymorphism and sexual dimorphism is developed. This notation is used to examine the properties of all morphism transformations possible from the minimal expressions of the nine morphism categories, as reached through defined minimum step changes. The significance of such pathway models is analysed in terms of general properties of butterfly polymorphism. The potential use of pathway models in evolutionary studies is briefly discussed, mainly with respect to phylogenetics, and ideas on the evolution of genetic dominance.     

The ilvIH operon of Escherichia coli K-12. Identification of the gene products and recognition of the translational start by polypeptide microsequencing

The ilvI and ilvH gene products were identified physically by electrophoretic analysis of in vivo-labelled polypeptides produced in minicells from plasmids carrying the wild-type ilvIH operon of Escherichia coli K-12 and derivatives of it. An analysis of the distribution of methionine residues in the amino-terminal portion of micro-quantities of the ilvI product eluted from gel showed that the translational start of the ilvI gene is the promoter-proximal one of three putative methionine codons predicted from the DNA sequence.     

Thyroid hormones selectively modulate human alcohol dehydrogenase isozyme catalyzed ethanol oxidation

Thyroid hormones are potent, instantaneous, and reversible inhibitors of ethanol oxidation catalyzed by isozymes of class I and II human alcohol dehydrogenase (ADH). None of the thyroid hormones inhibits class III ADH. At pH 7.40 the apparent Ki values vary between 55 and 110 microM for triiodothyronine, 35 and greater than 200 microM for thyroxine, and 10 and 23 microM for triiodothyroacetic acid. The inhibition is of a mixed type toward both NAD+ and ethanol. The binding of the thyroid hormone triiodothyronine to beta 1 gamma 1 ADH is mutually exclusive with 1,10-phenanthroline, 4-methylpyrazole, and testosterone, identifying a binding site(s) for the thyroid hormones, which overlap(s) both the 1,10-phenanthroline site near the active site zinc atom and the testosterone binding site, the latter being a regulatory site on the gamma-subunit-containing isozymes and distinct from their catalytic site. The inhibition by thyroid hormones may have implications for regulation of ADH catalysis of ethanol and alcohols in the intermediary metabolism of dopamine, norepinephrine, and serotonin and in steroid metabolism. In concert with other hormonal regulators, e.g., testosterone, the rate of ADH catalysis is capable of being fine tuned in accord with both substrate and modulator concentrations.     

The disposition of citric acid cycle intermediates by isolated rat heart mitochondria

The mechanism of depletion of tricarboxylic acid cycle intermediates by isolated rat heart mitochondria was studied using hydroxymalonate (an inhibitor of malic enzymes) and mercaptopicolinate (an inhibitor of phosphoenolpyruvate carboxykinase) as tools. Hydroxymalonate inhibited the respiration rate of isolated mitochondria in state 3 by 40% when 2 mM malate was the only external substrate, but no inhibition was found with 2 mM malate plus 0.5 mM pyruvate as substrates. In the prescence od bicarbonate, arsenite and ATP, propionate was converted to pyruvate and malate at the rates of 14.0 ± 2.9 and 2.8 ± 1.8 nmol/mg protein in 5 min, respectively. Under these conditions, 0.1 mM mercaptopicolinate did not affect this conversion, but 2 mM hydroxymalonate inhibited pyruvate formation completely and resulted in an accumulation of malate up to 13.2 ± 2.9 nmol/mg protein. No accumulation of phosphoenolpyruvate was found under any condition tested. It is concluded that malic enzymes but not phosphoenolpyruvate carboxykinase, are involved in conversion of propionate to pyruvate in isolated rat heart mitochondria.     

Local Conformation and Dynamics of Isoleucine in the Collagenase Cleavage Site Provide a Recognition Signal for Matrix Metalloproteinases

The mechanism by which enzymes recognize the “uniform” collagen triple helix is not well understood. Matrix metalloproteinases (MMPs) cleave collagen after the Gly residue of the triplet sequence Gly∼[Ile/Leu]-[Ala/Leu] at a single, unique, position along the peptide chain. Sequence analysis of types I-III collagen has revealed a 5-triplet sequence pattern in which the natural cleavage triplets are always flanked by a specific distribution of imino acids. NMR and MMP kinetic studies of a series of homotrimer peptides that model type III collagen have been performed to correlate conformation and dynamics at, and near, the cleavage site to collagenolytic activity. A peptide that models the natural cleavage site is significantly more active than a peptide that models a potential but non-cleavable site just 2-triplets away and NMR studies show clearly that the Ile in the leading chain of the cleavage peptide is more exposed to solvent and less locally stable than the Ile in the middle and lagging chains. We propose that the unique local instability of Ile at the cleavage site in part arises from the placement of the conserved Pro at the P₃ subsite. NMR studies of peptides with Pro substitutions indicate that the local dynamics of the three chains are directly modulated by their proximity to Pro. Correlation of peptide activity to NMR data shows that a single locally unstable chain at the cleavage site, rather than two or three labile chains, is more favorable for cleavage by MMP-1 and may be the determining factor for collagen recognition.     

Choline Administration Elevates Brain Phosphorylcholine Concentrations

Abstract: The phosphorylcholine concentration of rat brain rises and falls in response to parallel changes in the concentration of circulating choline. A single oral dose of choline chloride (20 mmol/kg) elevated whole-brain concentrations of both choline and phosphorylcholine 5 h after administration; a greater proportion of exogenously administered choline was retained by the brain in its phosphorylated form than as the free arnine. Striatal phosphorylcholine concentrations were elevated within 2 h of choline administration and continued to be significantly greater than control values for up to 34 h after treatment. The response of striatal choline levels to exogenous choline was of shorter duration than that of phosphorylcholine and was correlated with a significant increase in striatal acetylcholine concentrations. The consumption of a choline-free diet for 7 days lowered both serum choline and striatal phosphorylcholine concentrations, but had no effect on striatal choline or acetylcholine. These results suggest that choline kinase is unsaturated by its substrate in vivo and may thus serve to modulate the response of brain choline concentrations to alterations in the supply of circulating choline.     

Mathematical model of the activation of prothrombin by factor X a and factor V t

A mathematical model of prothrombin activation is being proposed which includes the feedback mechanism of thrombin and the alteration of factor V by thrombin. This model is in good agreement with experimental data for the dependence of the rate of thrombin formation on the concentrations of factors V and X _a . In particular, it correctly predicts the existence and location of a maximum in both of these cases.