Showing papers by "University of Los Andes published in 1974"

Sensitivity to Ampicillin and Cephalothin of Enzymes Involved in Wall Peptide Crosslinking in Escherichia coli K12, Strain 44

Abstract: After extraction of the membranes of Escherichia coli K12 strain 44 by Brij-36T, each of the four enzyme activities (natural transpeptidase, unnatural transpeptidase, carboxypeptidase and endopeptidase) of the wall peptide crosslinking system, occurs in two forms characterized by large differences in their sensitivity to ampicillin (but much smaller differences in their sensitivity to cephalothin). The fractionation of the enzyme activities into two groups of low and high sensitivity to ampicillin is achieved essentially by chromatography of the membrane extract on DEAE-cellulose.

Nerve conduction velocity in patients on long-term diphenylhydantoin therapy.

Abstract: Summary Motor conduction velocities along the median, ulnar, peroneal, and posterior tibial nerves and distal sensory latency of the median nerve were determined in 300 patients on diphenylhydantoin therapy who did not present clinical evidence of either peripheral neuropathy or toxicity. Slowed conduction was found in 156 patients (52%). Most frequent were prolonged sensory latency of the median nerve (44%) and motor conduction in the legs (33%). Abnormal findings were more frequent in patients over 20 yr of age, when the dose was 4.5 mg/kg or more and the duration of medication 4 yr or more. Resume Chez 300 patients traites par la diphenylhydantoihe et ne presentant aucun signe clinique de neuropathie peripherique ou d'intoxication, on a mesure la vitesse de conduction motrice des nerfs median, cubital, peronier et tibial posterieur, ainsi que la latence sensitive distale du nerf median. Chez 156 patients (52%) la vitesse de conduction etait ralentie. On a trouve le plus souvent un allongement de la latence sensitive du median (44%) et une diminution de la vitesse de conduction motrice au niveau des jambes (33%). Les valeurs anormales etaient plus frequentes chez les malades âges de plus de 20 ans quand la dose de diphenylhydantoihe etait de 4.5 mg/kg au plus et que le traitement durait depuis 4 ans ou plus. Zusammenfassung Bei 300 mit Diphenylhydantoin behandelten Patienten, die keine klinischen Symptome einer peripheren Neuropathie oder von Toxizitat zeigten, wurde die Nervenleitgeschwindigkeit des Nervus medianus, Ulnaris, Peronaeus und des Nervus tibialis posterior und zudem die distale sensorische Latenz des Nervus medianus bestimmt. Bei 156 Patienten, entsprechend 52%, war die NLG verlangsamt. Am haufigsten war die sensorische Latenz des Nervus medianus (44%) und die motorische Nervenleitgeschwindigkeit in den Beinen (bei einem Drittel) verlangert. Anormale Befunde waren haufiger bei Patienten uber 20 Jahren, bei einer Dosierung von 4.5 mg pro kg Korpergewicht oder mehr und bei Behandlungszeiten von 4 oder mehr Jahren. Resumen Se determineo la velocidad de conduccion motora de los nervios mediano, ulnar, peroneal y tibial posterior, asi como la latencia sensorial distal del mediano en 300 pacientes que se encontraban en tratamiento con Difenilhidantoina y que no presentaban evidencia de neuropatia periferica o de intoxicacion. En 156 pacientes (52%) se eonstato disminucion de la conduccion nerviosa. El hallazgo mas frecuente fue el aumento de la latencia sensorial del n. mediano (44%) y una disminucion de la velocidad de conduccion motora en las piernas (33%). Los hallazgos anormales fueron mas frecuentes en pacientes mayores de 20 anos, cuando la dosificacion era superior a 4.5 mg/kg de peso, y cuando la duracion del tratamiento fue mayor de 4 anos.

Binding of beta-lactam antibiotics to the exocellular DD-carboxypeptidase-transpeptidase of Streptomyces R39

Abstract: Benzylpenicillin and cephaloridine reacted with the exocellular DD-carboxypeptidasetranspeptidase from Streptomyces R39 to form equimolar and inactive antibiotic-enzyme complexes. At saturation, the molar ratio of chromogenic cephalosporin 87-312 to enzyme was 1.3: 1, but this discrepancy might be due to a lack ofaccuracy in the measurement of the antibiotic. Spectrophotometric studies showed that binding of cephaloridine and cephalosporin 87-312 to the enzyme caused opening of their /J-lactam rings. Benzylpenicillin and cephalosporin 87-312 competed for the same site on the free enzyme, suggesting that binding of benzylpenicillin also resulted in the opening of its 8-lactam ring. In Tris-NaCl-MgCI2 buffer at pH7.7 and 37° C, the rate constants for the dissociation of the antibiotic-enzyme complexes were 2.8 x 10-, 1.5 x 10-6 and 0.63 x 106s1 (half-lives 70, 130 and 300h) for benzylpenicillin, cephalosporin 87-312 and cephaloridine respectively. During the process, the protein underwent reactivation. The enzyme that was regenerated from its complex with benzylpenicillin was as sensitive to fresh benzylpenicillin as the native enzyme. With ['4C]benzylpenicillin, the released radioactive compound was neither benzylpenicillin nor benzylpenicilloic acid. The Streptomyces R39 enzyme thus behaved as a,8-lactam-antibiotic-destroying enzyme but did not function as a ,8-lactamase. Incubation at 37° C in 0.01 M-phosphate buffer, pH7.0, and in the same buffer supplemented with sodium dodecyl sulphate caused a more rapid reversion of the ['4C]benzylpenicillin-enzyme complex. The rate constants were 1.6 x 10-5 s-1 and 0.8 x 10-4s-1 respectively. Under these conditions, however, there was no concomitant reactivation of the enzyme and the released radioactive compound(s) appeared not to be the same as before. The Streptomyces R39 enzyme and the exocellular DD-carboxypeptidase-transpeptidase from Streptomyces R61 appeared to differ from each other with regard to the topography of their penicillin-binding site.

The depolarization of electromagnetic radiation in a random medium: evolution of the Stokes parameters

Abstract: (1974). The Depolarization of Electromagnetic Radiation in a Random Medium: Evolution of the Stokes Parameters. Optica Acta: International Journal of Optics: Vol. 21, No. 9, pp. 721-735.

Intento de Aislamiento del Paracoccidioides brasiliensis del suelo

Abstract: Cuarenta y cinco muestras de tierra, preferentemente de cafetales a mas de 500 m de altitud sobre el nivel del mar, de varias regiones de Venezuela fueron inoculadas por via endovenosa en ratones No pudo aislarse elParacoccidioides brasiliensis Se discuten brevemente las posibles causas de los resultados negativos y se proponen otras technicas para seguir intentando la determinacion del habitat deParacoccidioides brasiliensis

Estimation of solubility parameters of nonelectrolytes

Abstract: THE Hildebrand approach1,2 provides an explanation of the solubility of nonelectrolytes based on a thermodynamic method. In this method used for the estimation of solubility, it is assumed that each molecule possesses a characteristic potential energy based on intermodular forces which may be described as the cohesive energy density. The latter may be defined as the potential energy of 1 cm3 of liquid or the energy required to separate all molecules in a unit volume of liquid. This value is zero when the molecules are randomly dispersed in a solution.

Theory of the Compensation-Induced Parity-Forbidden Excitation Spectra of Shallow Impurities in Semiconductors

Abstract: An approximate formula for the line shape for the compensation-induced parity-forbidden 1s–2s optical absorption of shallow hydrogen-like impurities in semiconductors is given in the limit of small compensations. The unusual “camel-back” structure of the absorption peak is predicted.