A conformational approach to the study of the dynamics of enzyme inhibition: studies on thermolysin

The preferred conformations of β-phenylpropionyl-l-phenylalanine (β-PPP) and $\text{N-}\text{carbobenzoxy-}\text{l}\text{-phenylalanine}$ (Cb_z-Phe), two inhibitors of thermolysin, have been determined by computing potential energy using empirial potential energy functions. Of the 15 to 20 conformations that are favoured for each of these inhibitors only a few have the right conformation to reach the active site of the enzyme. The conformer of β-PPP that initiates binding with the enzyme is different from the bound one, while for Cb_z-Phe the bound and initiating conformers are quite similar. Thus, β-PPP favours the ‘induced fit’ model while Cb_z-Phe follows the ‘lock and key’ model of binding. The inhibitors differ in their alignment at the active site.     

THE FLORAL ANATOMY OF KOEBERLINIA ZUCC: SYSTEMATIC IMPLICATIONS

The in toto pattern of the floral vasculature in Koeberlinia Zucc, is distinctive. The median vascular trace to each sepal is concrescent with the antesepalous stamen trace forming a trace complex. Each petal trace is concrescent with the nearest antestaminal trace, and this common trace is in turn concrescent basally with the common basal supply to the adjacent sepal margins. The ventral carpellary bundles and the ovular traces of the two carpels are arranged for part of the ventral carpellary system into an essentially continuous hollow stele-like cylinder and many of the ovular vascular supplies originate from this strand. All vascular concrescences are congenital. Comparisons of the morphological and floral vasculature characters of Koeberlinia with those of its various putative allies revealed that there are no substantial reasons for linking Koeberlinia with Canotia, Celastraceae, Rutaceae, Simaroubaceae, or Zygophyllaceae. The in toto floral vascular structure of Koeberlinia is closely similar to that of the Caryophyllaceae and dissimilar to that of the Capparaceae. Several qualitative characters of the secondary xylem of Koeberlinia differ from those of the Capparaceae, yet certain important ones are similar. Many of the morphological characters of Koeberlinia are similar to those of the Capparaceae as well as the Caryophyllaceae, yet certain critically important ones strongly indicate a relation of Koeberlinia to the Capparaceae: occurrence of myrosin cells, capparaceous pollen, capparaceous ovular characters. To include Koeberlinia within either of these families is unwise, but the writers are inclined to retain Koeberlinia in a monogeneric family within the larger Capparales.     

EspP,an Extracellular Serine Protease from Enterohemorrhagic E. coli,Reduces Coagulation Factor Activities,Reduces Clot Strength,and Promotes Clot Lysis

Background

EspP (E. coli secreted serine protease, large plasmid encoded) is an extracellular serine protease produced by enterohemorrhagic E. coli (EHEC) O157:H7, a causative agent of diarrhea-associated Hemolytic Uremic Syndrome (D+HUS). The mechanism by which EHEC induces D+HUS has not been fully elucidated.

Objectives

We investigated the effects of EspP on clot formation and lysis in human blood.

Methods

Human whole blood and plasma were incubated with EspP^WT at various concentrations and sampled at various time points. Thrombin time (TT), prothrombin time (PT), and activated partial thromboplastin time (aPTT), coagulation factor activities, and thrombelastgraphy (TEG) were measured.

Results and Conclusions

Human whole blood or plasma incubated with EspP^WT was found to have prolonged PT, aPTT, and TT. Furthermore, human whole blood or plasma incubated with EspP^WT had reduced activities of coagulation factors V, VII, VIII, and XII, as well as prothrombin. EspP did not alter the activities of coagulation factors IX, X, or XI. When analyzed by whole blood TEG, EspP decreased the maximum amplitude of the clot, and increased the clot lysis. Our results indicate that EspP alters hemostasis in vitro by decreasing the activities of coagulation factors V, VII, VIII, and XII, and of prothrombin, by reducing the clot strength and accelerating fibrinolysis, and provide further evidence of a functional role for this protease in the virulence of EHEC and the development of D+HUS.     

MORPHOLOGICAL STUDIES OF THE NYMPHAEACEAE (SENSU LATO). XIII. CONTRIBUTIONS TO THE VEGETATIVE AND FLORAL STRUCTURE OF CABOMBA

Six species of Cabomba have been examined although the anatomy of the vegetative axes is based on the study of only C. caroliniana and C. palaeformis. A plant consists of an erect short shoot with decussate leaves which bears axillary flowering shoots and rhizomes. A rhizome bears decussate leaves and may also form axillary flowering shoots or turn upward and become a new short shoot. The phyllotaxies of the flowering shoots are proximately decussate or ternate (C. piauhyensis). The flowering shoots with decussate phyllotaxy change to 1/3 phyllotaxy distally; they bear axillary flowers proximally, and extra-axillary flowers distally. Flowering shoots with ternate phyllotaxy do not change distally but each produces first axillary and then extra-axillary flowers. Decussate vegetative axes and flowering shoots have four vascular bundles; ternate vegetative axes and flowering shoots have six vascular bundles, distantly paired into two or three vascular bundle-pairs, respectively. An elliptical vascular plexus occurs at each node. Each leaf receives one bundle-pair from one trace and each flower three bundle-pairs. A two-level receptacular vascular plexus occurs in flowers; the proximal, larger portion provides traces to perianth and stamens and the distal, smaller portion becomes carpellary traces. Each of the three sepals typically receives five branch traces from a basal principal trace, and each of the three petals receives, typically, three branch traces from a basal principal trace. Sepals and petals generally occur in a single, basally connate whorl. Each stamen receives one trace. Each stamen of three-stamen flowers is opposite a petal; each stamen of six-stamen flowers is aligned with an interval between a petal and adjacent sepal. Each staminal trace, which is just above the principal petal trace, in a three-petal flower, is frequently adnate to the latter trace. Each carpel receives one principal trace from the distal, small extension of the receptacular plexus, and each principal trace becomes three conventional veins of a carpel. Ovules may be borne directly over one of the veins or in any position between veins and are supplied by branches of the nearest vein or nearest two veins. All traces, ovular supply veins and the proximal portions of all veins are amphicribral. The several anatomical and morphological differences in vegetative axes and flowers between Cabomba and Brasenia suggest a greater taxonomic distance between the two genera than commonly supposed. It is suggested that extra-axillary flowers in 1/3 helical and ternate flowering shoots of Cabomba might be advantageous in preventing anthesis of flowers beneath peltate leaves. The aberrant position might be the initial evolutionary step toward what, in other nymphaeaceous genera, has shifted each flower to an adjacent helix. It is proposed that the zigzag stem accompanying the trigonal and sympodial flowering shoots may offer greater stability and floatability in water than the monopodial form. Several suggestions are offered for the variability of ovular positions: 1) the variability is a vestige of former laminar placentation in conduplicate carpels; 2) it is a vestige of a primitive condition antedating the current close association of ovules with ventral carpellary veins; 3) it is an early stage of evolution which might have terminated in laminar placentation and cantharophily, but which was replaced by a trend toward myophily.     

Protective Effect of Selenium on Nicotine-Induced Testicular Toxicity in Rats

Effect of exogenous selenium at a dose of 10 mug/kg body weight on the testicular toxicity induced by nicotine in rats was investigated. Male albino rats were maintained for 60 days as follows: (1) control group (normal diet), (2) nicotine group (0.6 mg /kg body weight), (3) selenium (10 microg/kg body weight), and (4) nicotine (0.6 mg/kg body weight) + selenium (10 microg/ kg body weight). Administration of nicotine caused reduction in sperm count and sperm motility. Activity of HMG CoA reductase and concentration of cholesterol were increased in the testes of the nicotine administered group. Activities of testicular enzymes 3beta hydroxysteroid dehyrogenase (3 betaHSD), 17beta hydroxysteroid dehyrogenase (17 betaHSD) were decreased. Levels of testosterone in the serum were also reduced. However, the extent of these alterations was lesser in the group administered with nicotine along with selenium. Analysis of plasma revealed reduced quantity of cotinine in the group co-administered with nicotine along with selenium in comparison with the nicotine group. Nondetectable levels of nicotine were present in the co-administered group. This indicates altered metabolism of nicotine when administered along with selenium.     

Effects function analysis of ELF magnetic field exposure in the electric utility work environment

The incomplete understanding of the relation between power-frequency fields and biological responses raises problems in defining an appropriate metric for exposure assessment and epidemiological studies. Based on evidence from biological experiments, one can define alternative metrics or effects functions that embody the relationship between field exposure patterns and hypothetical health effects. In this paper, we explore the application of the “effects function” approach to occupational exposure data. Our analysis provides examples of exposure assessments based on a range of plausible effects functions. An EMDEX time series data set of ELF frequency (40–800 Hz) magnetic field exposure measurements for electric utility workers was analyzed with several statistical measures and effects functions: average field strength, combination of threshold and exposure duration, and field strength changes. Results were compared for eight job categories: electrician, substation operator, machinist, welder, plant operator, lineman/splicer, meter reader, and clerical. Average field strength yields a different ranking for these job categories than the ranks obtained using other biologically plausible effects functions. Whereas the group of electricians has the highest exposure by average field strength, the group of substation operators has the highest ranking for most of the other effects functions. Plant operators rank highest in the total number of field strength changes greater than 1 μT per hour. The clerical group remains at the lowest end for all of these effects functions. Our analysis suggests that, although average field strength could be used as a surrogate of field exposure for simply classifying exposure into “low” and “high,” this summary measure may be misleading in the relative ranking of job categories in which workers are in “high” fields. These results indicate the relevance of metrics other than average field strength in occupational exposure assessment and in the design and analysis of epidemiological studies. Bioelectromagnetics 18:365–375, 1997. © 1997 Wiley-Liss, Inc.     

Phosphoribosyltransferase superfamily: A comparative structural analysis

Purine phosphoribosyltransferases are members of a group of enzymes that are responsible for the formation of purine, pyrimidine and pyridine nucleotides. One feature of this family is a flexible loop, which is involved in the catalytic mechanism. This loop is variable both in sequence and structure in the phosphoribosyltransferase family. This paper describes the modelling and validation of a model of Plasmodium falciparum hypoxanthine-guanidine- phosphoribosyltransferase in an open conformation. A comparison of this model with 3D-structures of other members of the phosphorybosyltransferase family has allowed an assessment of the role of the open and closed conformations of the loop in the catalytic mechanism.