Active site kinetics of horse serum cholinesterase

Horse serum Cholinesterase hydrolyzes choline and p-nitrophenol esters at different rates. Deacylation and acylation seem to be the rate-limiting step for charged and uncharged substrates respectively. Activation energy is similar for the acetic, propionic, and butyric esters of thiocholine, but it is higher for p-nitrophenylpropionate. Inhibition by the tetramethyl-ammonium ion is competitive. Tetraethyl-, tetrapropyl-, and tetrabutyl-ammonium ions are mixed-type inhibitors. The pH studies demonstrated the existence of a residue, pK = 6.33, involved in catalysis.     

Ultrastructural changes in Blastomyces dermatitidis after in vitro exposure to lidocaine

Electron microscopic examination of yeasts of Blastomyces dermatitidis, exposed in vitro to concentrations of lidocaine that occur when the drug is used for topical anesthesia, showed that lidocaine rapidly damaged intracellular structures. The extent of damage was dependent on the concentration of drug and length of exposure. The observed ultrastructural changes were very similar to those reported for other drugs that directly damage membranes. This relationship suggests that the antifungal effect of lidocaine is the result of direct membrane damage.     

Adenine deaminase of a eukaryotic animal cell,Crithidia fasciculata

Adenine deaminase (adenine aminohydrolase, EC 3.5.4.2) has been found to occur in Crithidia fasciculata with a specific activity higher than that of the same enzymes of bacteria and yeasts. It is remarkable for its stability to heat, exhibiting no appreciable loss of activity after 60 min at 55 °C. It occurs in the soluble portion of cell extracts but can be released into the suspending medium by osmotic and/or cold shock.     

Glycoprotein reductions in the adipocyte cytoplasmic membrane from obese Zucker rats

The adipocyte cytoplasmic membranes from lean and obese Zucker rats were analyzed. A reduction in the galactose-containing glycoproteins was demonstrated from adipocyte cytoplasmic membranes of obese rats. A compensatory increase was observed in several membrane proteins which did not contain carbohydrate. This reduction was observed in obese rats at 5 and 16 weeks old.     

Disease lesion mimics in maize: I. Effect of genetic background,temperature, developmental age,and wounding on necrotic spot formation with Les1

Les1, a dominant gene of maize (Zea mays L.), results in the production of necrotic leaf spots. Expression of this trait is temperature sensitive, and the nonpermissive temperature for expression is determined by the genetic background in which the gene is placed. Exposure to nonpermissive conditions for 24–48 hr will induce lesion production in the most sensitive genotype. Lesions form first at the leaf tip, the oldest part of the leaf, and progress basipetally through fully expanded tissue. Leaves excised from plants grown at either permissive or nonpermissive temperatures and placed in water, gibberellic acid, or abscisic acid solutions form no new lesions at either 20 or 30°C, and the leaves senesce rapidly. However, when leaves excised from normal and Les1 plants are placed in kinetin, senescence is delayed and numerous lesions develop at 20°C on Les1 plants. Our results suggest that there is a developmental time window during which maize leaf cells can be induced to form lesions: cells must be fully elongated but not yet senescent. This hypothesis is strengthened by the observation that pinprick wounding of leaves induces lesions only in a band of tissue approximately 2 days younger than the area of the leaf currently producing lesions. Various models for the action of Les1 in causing discrete lesion formation are discussed.     

Possible role of rat fatty acid-binding proteins in the intestine as carriers of phenol and phthalate derivatives

Fatty acid-binding proteins of hepatic and intestinal type and gastrotropin-like protein (GTLP) were purified from rat intestinal cytosol by Sephadex G-75 gel filtration and DEAE-cellulose, CM-cellulose, and hydroxylapatite chromatographies. In addition to fatty acids, butylated hydroxytoluene (BHT), phthalate dibutyl, and di(2-ethylhexyl) esters (DBP and DEHP) were identified by gas liquid chromatography and mass spectrometry as endogenous ligands from the extract of either fatty acid-binding protein superfamily. These protein families in the intestine may have an important role as carriers in the initial step of arresting these exogenous pollutants.     

Structural Characteristics of the Short-Tail Fibers of T4 Bacteriophage

The characteristics of pure preparations of short-tail fibers of bacteriophage T4 have been studied in the optical and electron microscope. Three main structures were observed: 1) spheres of 8.1 nm diameter; 2) fibers 43 nm long and 3.8 nm thick; and 3) fibers 54 nm long and 3.2 nm thick. Both types of fibers exhibited a regular beaded appearance. The 43-nm fibers were the most abundant structure. During the process of purification of the short-tail fibers, the formation of aggregates was observed each time the material containing the short-tail fibers was dialyzed against saline solutions. These aggregates became increasingly fibrous (as observed in the optical microscope) as the material used was increasingly enriched in short-tail fibers. Finally, most of the aggregates were of the fibrous type when they were formed from a purified preparation of short-tail fibers. In the electron microscope, it was found that the filamentous aggregates were organized in well-defined bundles. The amino acid composition of the highly purified short-tail fibers was also determined. Among the known fibrous proteins, the ones that most resemble the amino acid composition of the short-tail fibers are actin and fibrinogen. These observations are discussed in relation to the T4 short-tail fiber structure and their localization on the hexagonal baseplate of the T4 tail structure.     

The Impact of Random and Lineal Fission on the Genetic Divergence of Small Human Groups: A Case Study among the Yanomama

Most of the genetic divergence that currently separates populations of Homo sapiens must have arisen during that long period when the local village (or band) was the basic unit of biological evolution. Studies of tribally intact Amerindian groups exhibiting such small-group organization have demonstrated marked genetic divergence between nearby villages. Some of this genetic radiation can be attributed to the effects of random genetic drift over time within these small demes. Some of it, however, might be better ascribed to the consequences of nonrandom genetic assortment at the time of village fission, a recurring event for such groups. Even random genetic assortment at the time of fission would lead to some genetic divergence, due to the finite size of the parent gene pool. We term the genetic consequences of random assortment the random fission effect. Routinely, village fission occurs along family lines, leading to even greater genetic divergence between the daughter villages. We use the term lineal fission effect to describe the genetic consequences of nonrandom assortment and contrast these results with those derived from random assortment.——A formal treatment of random and lineal fission effects is developed, first for the single-locus case, then for the multiple-locus extension. Using this formulation, three Yanomama fission events were examined. Fission in the Yanomama often involves a great deal of mutual hostility between the two factions, so that subsequent gene flow between the two daughter villages is minimal. The first two examples are typical of the Yanomama behavior norm, and are accompanied by a minimum of subsequent gene flow between the daughter villages. In these two cases, the observed divergence values are very large and are also very unlikely under random fission. The lineal fission effect is pronounced. The net impact of lineal fission is to reduce the effective size of the village at the time of fission by a factor of four, relative to expectation from random fission. The third example, however, involved an unusually amicable split of a village, followed by free genetic exchange between the fission products. This "friendly fission" yields an observed divergence value not much in excess of the expectation from random fission.—The long-term consequences of such fission bottlenecks in effective population size are discussed for both intra- and inter-tribal genetic diversity. It appears that the rate of genetic divergence for tribal and subtribal groups may have been somewhat greater than would be expected from classical drift arguments.