Biomedical subjects
B Mendez
Publications and source records attributed to B Mendez.
Role of the CheW protein in bacterial chemotaxis: overexpression is equivalent to absence.
The cheW gene from Escherichia coli has been cloned an inducible promoter, and the effects of the overproduction of the CheW protein on chemotactic behavior and receptor covalent modification have been examined. Plasmids that contain the cheW gene behind a regulatable promoter complement a cheW mutation when the CheW protein is produced at low levels. However, when the CheW protein is greatly overproduced in either a wild-type strain or a cheW mutant, chemotaxis is greatly inhibited, cheW null mutant cells swim smoothly as if they were constantly responding to an attractant. Surprisingly, cells in which the CheW protein is overproduced also swim smoothly. The behavioral defect produced by overproduction of the CheW protein does not require the presence of the cheR, cheB, or cheZ gene. Receptor demethylation is also inhibited by overproduction of the CheW protein, as it is by a mutation in the cheW gene or a response to an attractant. In all respects, therefore, overproduction of the CheW protein has the same consequences as does a mutation in the cheW gene or a response to an attractant. A model involving two states of the CheW protein is proposed to explain its role in bacterial chemotaxis.
Acetylcholinesterase like that of skeletal muscle in smooth muscle reinnervated by a motor nerve.
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The representations of the visual field on the posterior cortex of Octodon degus.
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[Construction of derivatives of lambda phage carrying the lamB gene inserted downstream from the promotors of the lactose operon].
The expression of gene lamB, the structural gene for the lambda receptor in E. coli K-12, has been put under the control of the promoter of the lactose operon. This has been done by in vitro recombination using vectors which are derivatives of phage lambda.
Effects of different lipid sources in total parenteral nutrition on whole body protein kinetics and tumor growth.
This study examined the short-term effects of three total parenteral nutrition solutions, each containing a different lipid source, on host and tumor protein metabolism in a rat cancer model. Each diet contained 220 kcal/kg per day, including 2 g of nitrogen/kg per day and 50% of nonprotein calories as either a structured lipid of medium-chain triglycerides and fish oil, a physical mix of medium-chain triglycerides and fish oil, or Liposyn II, a long-chain triglyceride. A 3-day intravenous feeding infusion began on day 7 after tumor implantation. Tumor growth rate, nitrogen balance, energy expenditure, and plasma albumin, glucose, and free fatty acids were measured, and whole body protein kinetics and fractional synthetic rates in liver, muscle, and tumor tissues were assessed using a constant infusion of 14C-leucine. The results revealed that tumor growth rate was slowed in structured lipid-fed animals (p = .06, one-way analysis of variance) with significant increases in rates of tumor protein synthesis and tumor protein breakdown (p < .001, one-way analysis of variance). Although muscle fractional synthetic rates were significantly decreased in tumor-bearing animals (p < .05, two-way analysis of variance), the rates in structured lipid-fed animals were restored. Nitrogen balance improved significantly in structured lipid-fed animals. The results demonstrate that the source of lipid in total parenteral nutrition solutions can influence tumor and host protein metabolism, and that a structured lipid composed of medium-chain triglycerides and fish oil seems to improve protein metabolism in host tissue without stimulating tumor growth.
[R plasmids incompatibility groups in epidemic Salmonella (author's transl)].
The susceptibility to antimicrobial agents of 410 strains belonging to six serotypes of epidemic Salmonella (S. wien, S. saint-paul, S. panama, S. heidelberg, S. isangi and S. brandenburg) was studied. Resistance to one or more antibiotics was shown for 228 of these strains. Study of resistance transfer was investigated for 25 multiresistant strains of different epidemic origin. Resistance was coded for by conjugative R plasmids except in the case of S. brandenburg. From 20 strains of Salmonella, 39 plasmids were transferred to E. coli K12. Twenty-nine of these plasmids were classified into 7 incompatibility groups: IncFI, FII, I1, I2, N, C, M. These same groups were also found for 84 R plasmids from different enterobacteria. The "epidemic character" of these Salmonella serotypes does not seem to be associated with carriage of any particular R plasmid.