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A M Callahan

Publications and source records attributed to A M Callahan.

24 records · Page 2Linked to original sources
PubMed1990

Isolation and sequencing of cDNA clones encoding ethylene-induced putative peroxidases from cucumber cotyledons.

A cDNA library from ethephon-treated cucumber cotyledons (Cucumis sativus L. cv. Poinsett 76) was constructed. Two cDNA clones encoding putative peroxidases were isolated by means of a synthetic probe based on a partial amino acid sequence of a 33 kDa cationic peroxidase that had been previously shown to be induced by ethylene. DNA sequencing indicates that the two clones were derived from two closely related RNA species that are related to published plant peroxidase sequences. Southern analysis indicates that there are 1-5 copies in a haploid genome of a gene homologous to the cDNA clones. The deduced amino acid sequences are homologous with a tobacco (55% sequence identity), a horseradish (53%), a turnip (45%), and a potato (41%) peroxidase. The cloned sequences do not encode the 33 kDa peroxidase from which the original synthetic probe was been derived, but rather other putative peroxidases. An increase in the level of mRNA is evident by 3 hours after ethephon or ethylene treatment and plateaus by 15 hours.

Amino Acid Sequence↗
PubMed1987

Chemotaxis in Escherichia coli: construction and properties of lambda tsr transducing phage.

The tsr gene of Escherichia coli, located at approximately 99 min on the chromosomal map, encodes a methyl-accepting protein that serves as the chemoreceptor and signal transducer for chemotactic responses to serine and several repellents. To determine whether any other chemotaxis or motility genes were located in the tsr region, we constructed and characterized two lambda tsr transducing phages that each contain about 12 kilobases of chromosomal material adjacent to tsr. lambda tsr70 carries sequences from the promoter-proximal side of tsr; lambda tsr72 carries sequences from the promoter-distal side of tsr. Restriction maps of the bacterial inserts in these phages and Southern hybridization analyses of the bacterial chromosome indicated that the tsr gene is transcribed in the counterclockwise direction on the genetic map. Insert deletions were isolated in lambda tsr70 and transferred into the host chromosome to examine the null phenotype of tsr. All such strains exhibited wild-type swimming patterns and chemotactic responses to a variety of stimuli, but were specifically defective in serine taxis and other Tsr-mediated responses. In addition, UV programming experiments demonstrated that Tsr and several of its presumptive degradation products were the only bacterial proteins encoded by lambda tsr70 and lambda tsr72 that required host FlbB/FlaI function for expression. These findings indicate that there are probably no other chemotaxis-related genes in the tsr region. A series of tsr point mutations were isolated by propagating lambda tsr70 on a mutD host and used to construct a fine-structure map of the tsr locus. These mutations should prove valuable in exploring structure-function relationships in the Tsr transducer.

Bacterial Proteins↗
PubMed1985

The application of enzyme-linked immunosorbent assays (ELISA) to neuropeptides.

Procedures are presented for routine evaluation of antibody specificity, titre, and quantitation of antigen levels in tissue extracts without the use of radiolabeled probes. A colorimetric, enzyme-linked immunosorbent assay (ELISA) is described for general use with neuropeptides, using neurotensin as a primary example. These assays use rabbit anti-neurotensin immune serum which is colorimetrically identified after combination with an alkaline phosphatase-conjugated, affinity purified, goat anti-rabbit IgG and reaction with the chromogenic substrate, p-nitrophenyl phosphate. Because the principle of these methods can be adapted for use with various proteins and neuropeptides, they should find widespread applicability in neurobiology.

Alkaline Phosphatase↗
PubMed1985

Genetics of methyl-accepting chemotaxis proteins in Escherichia coli: cheD mutations affect the structure and function of the Tsr transducer.

The tsr gene specifies a methyl-accepting membrane protein involved in chemotaxis to serine and several repellent compounds. We have characterized a special class of tsr mutations designated cheD which alter the signaling properties of the Tsr transducer. Unlike tsr null mutants, cheD strains are generally nonchemotactic, dominant in complementation tests, and exhibit a pronounced counterclockwise bias in flagellar rotation. Several lines of evidence showed that cheD mutations were alleles of the tsr gene. First, cheD mutations were mapped into the same deletion segments as conventional tsr mutations. Second, restriction site analysis of the transducing phage deletions used to construct the genetic map demonstrated that the endpoints of the deletion segments fell within the tsr coding sequence. Third, a number of the cheD mutants synthesized Tsr proteins with slight changes in electrophoretic mobility, consistent with alterations in Tsr primary structure. These mutant proteins were able to undergo posttranslational deamidation and methylation reactions in the same manner as wild-type Tsr protein; however, the steady-state level of Tsr methylation in cheD strains was very high. The methylation state of the Tar protein, another species of methyl-accepting protein in Escherichia coli, was also higher than normal in cheD strains, suggesting that the aberrant Tsr transducer in cheD mutants has a generalized effect on the sensory adaptation system of the cell. These properties are consistent with the notion that the Tsr protein of cheD mutants is locked in an excitatory signaling mode that both activates the sensory adaptation system and drowns out chemotactic signals generated by other transducer species. Further study of cheD mutations thus promises to reveal valuable information about the functional architecture of the Tsr protein and how this transducer controls flagellar behavior.

Bacterial Proteins↗
PubMedDate not supplied

Evaluating the clinical significance of drug interactions: a systematic approach.

Remembering the myriad of psychotropic drug interactions is extremely difficult. Nevertheless, by applying a systematic approach, the clinician can often predict the occurrence and time course of such interactions. Several factors must be considered when assessing the potential consequences. Drug-related factors that increase the risk for clinically significant interactions include a low therapeutic index or narrow therapeutic window, a multiplicity of pharmacological actions, and inhibition or inducement of cytochrome P450 enzymes. Next, patient-related factors that can increase the risk for significant drug interactions should be considered. These include genetically based variations in drug-metabolizing capacity, as well as advanced age, underlying medical illness, and comorbid substance abuse. Finally, the literature should be carefully reviewed to as-certain the potential clinical relevance of available data. If a clinically significant drug interaction appears likely to occur, the patient's clinical status should be followed closely; therapeutic drug monitoring should be used if applicable and dosage adjustments made accordingly. Rational polypharmacy requires an understanding of the pharmacological principles governing drug interactions and a knowledge of the factors that increase the likelihood of clinically significant variations in drug action. This will allow the clinician to maximize beneficial effects while minimizing the risk of adverse events.

Drug Interactions↗