W. A. Escobar

  • Citations Per Year
Learn More
Site-specific mutation of Glu-166 to Ala in beta-lactamase causes a millionfold reduction in catalytic activity toward both penicillin and cephalosporin substrates and results in the stoichiometric accumulation of a normally transient acyl-enzyme intermediate. Kinetic analysis indicated that substitution of Glu-166 by Ala leads to negligible effect on the(More)
In the beta-lactamase (penicillinase) of Bacillus licheniformis 749/C, site specific mutation of Glu166 to Ala caused a million-fold reduction of catalytic activity towards both penicillin and cephalosporin substrates and resulted in the stoichiometric accumulation of the acyl enzyme. The rate of deacylation generally slowed by as much as 10(-7) compared to(More)
Lys-234 has been postulated to participate in beta-lactamase catalysis by acting as an electrostatic anchor for the C3 carboxylate of penicillins [Herzberg, O., & Moult, J. (1987) Science 236, 694-701]. To test this hypothesis, site-directed mutagenesis was used to convert the Lys-234 in Bacillus licheniformis beta-lactamase into Glu-234 or Ala-234. The(More)
Glutamate-166 of the Bacillus licheniformis beta-lactamase was specifically mutated to aspartate and cysteine in order to probe the function of this residue in catalysis. In both cases, a large decrease in activity (kcat/Km was 3.5 x 10(-5) smaller for E166C and 1 x 10(-3) smaller for E166D than for the wild-type) was observed, although the kinetics for the(More)
Tyr-105 is a conserved residue in the Class A beta-lactamases and is in close proximity to the active-site. Tyr-105 in beta-lactamase from Bacillus licheniformis was converted into Phe by site-directed mutagenesis. This mutation caused no significant effect on the structure of the enzyme and had only small effects on the catalytic properties. In particular,(More)
The proposed model holds that, at its most fundamental level, visual awareness is quantized. That is to say that visual awareness arises as individual bits of awareness through the action of neural circuits with hundreds to thousands of neurons in at least the human striate cortex. Circuits with specific topologies will reproducibly result in visual(More)
beta-Lactamase from Bacillus licheniformis forms a stable compact intermediate state at low pH and moderate salt concentration (the A state), with properties consistent with a molten globule. A single cysteine residue was introduced into this class A beta-lactamase by site-directed mutagenesis at position 166. A spin label was attached to the thiol of this(More)
Neutralizing antibodies to polioviruses in cord blood of neonates born from 64 mothers under age 20 and in 53 mothers aged 30 years and over were investigated in order to know and compare the transfer to newborns of antibodies to polioviruses produced by live oral vaccine mainly and those antibodies induced by natural contact with wild poliovirus strains.(More)
  • 1