Problems in the determination of isoelectric points of beta lactamases]

Analytical isoelectric focusing in polyacrylamide gels and preparative electrofocusing in density gradients may give very different pI determination for the same beta lactamase. This difference seems due to a lack of enzyme migration in some parts of the cross-linked polyacrylamide gel. This migration appears easier in density gradient isoelectricfocusing, and thus this technique yields more significant absolute pI values. Analytical isoelectric focusing should only be used for comparison studies.     

A model of enzymatic kinetics]

In this Note, we study a system of differential equations representing the kinetics of an enzymatic reaction. For a closed system, and in the domain where it has a biological significance, it is shown that: (i) there exists a unique equilibrium point, which is an asymptotically stable point; (ii) if several enzymes act on the same substrates, the equilibrium values of the substrates concentrations take their values within the range of the equilibrium values achieved with each of these enzymes, (iii) the kinetics of the reaction can be approached by a single first-order differential equation, which may be seen as a generalization of the Michaelis equation.     

A fast osmotic transition method for the study of pulmonary transcapillary exchange: theoretical model]

A theoretical model allowed the simultaneous determination of the reflexion coefficients of capillary membrane to small hydrophilic molecules and of the ratios of their permeability to filtration coefficient. This was applied to dilution curves obtained after injection of a hypertonic solution containing a vascular tracer. The calculated variables did not depend on the capillary exchange surface area.     

A new method permitting the quantitative determination of virus present in surface waters]

With a 34% efficiency, not related to the amount of viruses, a simple and inexpensive apparatus allows quantitative recovery of enteroviruses from river-water.     

A simple method for the preparation of hydra chromosome spreads: introducing chromosome counts into hydra taxonomy

Summary A simple method to prepare chromosome spreads of hydra is described. Chromosome counts for a non-symbiotic brown hydra,Hydra vulgaris attenuata, and the Swiss strain of a symbiotic green hydra indicated a diploid number of about 2n=30 in each case. It is suggested that chromosome number may be used to define hydra species more precisely.This work was done while A. R. and M. R. were on leave in Oxford. We thank Prof. D. C. Smith F. R. S. for providing laboratory facilities. We wish to thank Prof. Smith and Dr A. E. Douglas for reading earlier drafts of this paper.     

A radio-immunoassay for the determination of thyroid stimulating hormone

Résumé Les auteurs présentent un dosage radio-immunologique quantitatif de la thyréostimuline. Les conditions optimales pour son application en vue de mesurer la TSH endogène sont étudiées. Cette méthode est très sensible et permet de mesurer jusqu'à 5µU de TSH non marquée. Les premiers résultats obtenus chez l'homme sont présentés.     

A BVAR model for the connecticut economy

A Bayesian vector autoregressive (BVAR) model is developed for the Connecticut economy to forecast the unemployment rate, nonagricultural employment, real personal income, and housing permits authorized. The model includes both national and state variables. The Bayesian prior is selected on the basis of the accuracy of the out-of-sample forecasts. We find that a loose prior generally produces more accurate forecasts. The out-of-sample accuracy of the BVAR forecasts is also compared with that of forecasts from an unrestricted VAR model and of benchmark forecasts generated from univariate ARIMA models. The BVAR model generally produces the most accurate short- and long-term out-of-sample forecasts for 1988 through 1992. It also correctly predicts the direction of change.     

A rapid,sensitive method for the determination of follicle-stimulating activity

Riassunto Gli Autori riportano un nuovo metodo di saggio sul topo di piccole quantità di ormone follicolo stimolante (FSH), basato sulla riduzione intravaginale del cloruro di 2,3,5-trifeniltetrazolio cloruro (TTC). È cosi possibile determinare quantitativamente in sole 30 h dosi di FSH almeno 50 volte inferiori a quelle valutabili con i metodi fino ad oggi proposti.     

A spectrophotometric method for the determination of 5-phosphoribosyl-1-pyrophosphate

Summary A new, sensitive, specific and simple spectrophotometric method for the determination of 5-phosphoribosyl-1-pyrophosphate (PRPP) is presented. PRPP is reacted with excess hypoxanthine in the presence of hypoxanthine-guanine phosphoribosyltransferase. At the end of the reaction, PRPP concentration is measured from the extent of conversion of hypoxanthine to inositate. The concentration of the purine base is determined spectrophotometrically in the presence of xanthine oxidase.     

A new method for determination of α-amylase

Zusammenfassung Für die Bestimmung der enzymatischen Aktivität der-Amylase wurde ein neues Substrat synthetisiert. Die Synthese kam in der Hauptsache durch die Farbstoffbindung an wasserlösliche Stärke und die anschliessende Vernetzung sowie durch den Zusatz von Diepoxid zustande.     

Quantitative determination of the activity of acid peptidases of industrial origin]

Reagent ninhydrine-Cd++, reacts with free alpha and epsilon amino groups of proteins. Horse-heart apomyoglobin was subjected to exhaustive succinylation, rendering the product non reactive to ninhydrine. The succinylglobin was submitted to enzyme digestion at pH 2.0, 4.0, 4.7 and 6.0. The commercially available enzymes contain mainly pepsin-like and chymosin-like enzymes. The enzymatic digests of succinyl-globin contain new free alpha-amino groups reacting with ninhydrin. Enzymatic digestion was performed under various condition (ratio E/S, pH). The results were compared to those obtained with synthetic substrate: PRO-HIS-LEU-SER-PHE(NO2)-NLEU-ALA-LEU-OME. The price of the synthetic substrate used, was more than 100 times the cost of succinyl-globin, thus the use of this substrate is a valuable tool for the quantitative estimation of peptidase activity in commercially available (pepsin, chymosin-like) enzymes.     

A rapid method for the purification of octopine dehydrogenase for the determination of cell metabolites

Summary Unlike other NAD⁺-dependent dehydrogenases, octopine dehydrogenase was not bound by blue Sepharose. A rapid 2-step purification procedure (gel filtration on Sephadex G-100 followed by affinity chromatography on blue Sepharose) resulted in a final preparation of octopine dehydrogenase which had a sp. act. of 65 units/mg protein and was free of contaminating NAD⁺-oxidoreductases. This preparation has been used successfully for the estimation of phospho-L-arginine, L-arginine and octopine in perchloric acid extracts.Supported by a grant from the Deutsche Forschungsgemeinschaft (Ga 241/1).     

A convenient cell for the determination of the electrophoretic velocity of microscopic particles

Zusammenfassung Es wird eine modifizierte Glaselektrophoresezelle von zylindrischem Querschnitt beschrieben, die in jedem Laboratorium leicht hergestellt werden kann. Der Vorteil der Modifikation hinsichtlich der Fokussierung und der Beweglichkeit wird besprochen.     

Detection of human antigens on the surface of mouse cells transformed by chromosome transfer]

Mouse embryo cells, transformed in vitro by the transfer of chromosomes from HeLa human tumour cells, express a surface antigen (s) also found on HeLa cells. This antigen(s), which has been detected both by indirect immunofluoresence and by a 125I-protein A binding assay, is not an antigen(s) shared by both Human and Mouse cells.     

A method for the determination of thrombocyte aggregation in circulating rat blood

Zusammenfassung Das Ausmass einer experimentell induzierten Thrombozytenaggregation im strömenden Blut wird kontinuierlich bestimmt durch Messung des Blutdrucks vor und hinter einem extrakorporal in den arteriellen Kreislauf der Ratte aufgenommenen Filter. Die Aggregation wird durch Infusion von Adenosindiphosphorsäure (ADP) vor dem Filter induziert. Die Aggregate schliessen das Filter teilweise ab, was zu Änderungen im Blutdruck vor und hinter dem Filter führt. Aus diesen Änderungen lässt sich das Mass der Aggregation ermitteln. Es wurde gefunden, dass dieses durch die ADP-Gabe bedingt wird.