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E Mendez

Publications and source records attributed to E Mendez.

69 records · Page 4Linked to original sources
PubMed1982

The complete amino acid sequence of human serum transferrin.

The complete amino acid sequence of human serum transferrin has been determined by aligning the structures of the 10 CNBr fragments. The order of these fragments in the polypeptide chain is deduced from the structures of peptides overlapping methionine residues and other evidence. Human transferrin contains 678 amino acid residues and--including the two asparagine-linked glycans--has an overall molecular weight of 79,550. The polypeptide chain contains two homologous domains consisting of residues 1-336 and 337-678, in which 40% of the residues are identical when aligned by inserting gaps at appropriate positions. Disulfide bond arrangements indicate that there are seven residues between the last half-cystine in the first domain and the first half-cystine in the second domain and therefore, a maximum of seven residues in the region of polypeptide between the two domains. Transferrin--which contains two Fe-binding sites--has clearly evolved by the contiguous duplication of the structural gene for an ancestral protein that had a single Fe-binding site and contained approximately 340 amino acid residues. The two domains show some interesting differences including the presence of both N-linked glycan moieties in the COOH-terminal domain at positions 413 and 610 and the presence of more disulfide bonds in the COOH-terminal domain (11 compared to 8). The locations of residues that may function in Fe-binding are discussed.

Amino Acid Sequence↗
PubMed1976

Chemistry of cholera toxin: the subunit structure.

The toxin of Vibrio cholerae was separated into two subunits by gel filtration on Sephadex G-75 in 5% formic acid. The subunits were designated A and B. Amino acid analysis indicated that subunit B corresponded to choleragenoid. Renatured subunit B was found to be antigenically identical to the whole molecule, whereas renatured subunit A was not. On reduction and S-carboxymethylation with [2-14C] iodoacetate in 8 m urea, subunit A separated into two polypeptides of unequal sizes, A1 and A2, with equal amounts of radioactivity. Subunit B, on the other hand, remained a single molecular species. Molecular weights of the polypeptides A1, A2, and B were estimated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate-urea buffer, in conjunction with amino acid analysis, to be 20,000, 7,500, and 9,500 daltons, respectively. The carboxyl terminal sequence of subunit B was found to be -Met-Ala-Asn. After treatment of toxin with cyanogen bromide, the peptide Ala-Asn could be isolated and quantitated. From this data the number of B polypeptides in a molecule of toxin was estimated as six.

Amino Acids↗
PubMedDate not supplied

A qualitative retrospective analysis of positive control data in developmental neurotoxicity studies.

Testing for neurodevelopmental effects commonly involves both functional and neuropathological assessments in offspring during and following maternal exposure. The use of positive controls in neurotoxicity screening has been advocated by numerous expert groups. Evaluation of positive control data allows evaluation of laboratory proficiency in detecting changes in the structure and function of the developing nervous system and comparison of the sensitivity of assessments in different studies and laboratories. This project surveyed approaches taken in contract and industrial laboratories in generating and providing these data. Positive control data submitted in support of 34 developmental neurotoxicity (DNT) studies from 16 different laboratories were summarized by test method for information on the following: age relevance of test subjects, the presence of a dose-response relationship, gender, group size, statistics, report quality, quality assurance, and the year the study was conducted. Endpoints included the following: developmental landmarks, clinical observations (CO), motor activity, startle response, learning and memory, qualitative neuropathology, and quantitative brain morphometry (linear measurements of selected brain regions). Results ranged from no positive control data for three laboratories, to one laboratory that submitted 17 separate positive control reports. The qualitative range was similarly broad, from excellent to poor. Various problems were identified, including the following: inappropriate report structure (e.g., copies of poster presentations), lack of individual data, inadequate methodological details, submission of very old data (>10 years) or data from completely different laboratories, use of inappropriate positive control chemicals or doses that were without effect, lack of statistical analysis, use of only one sex, and use of incompatibly aged animals. Analyses revealed that there were only 3 out of 16 laboratories that had submitted positive control data adequate for proficiency purposes for all of the major endpoints in the DNT study. Adequate positive control data are very useful in a weight-of-evidence approach to help determine the biological significance of results, and also to increase the confidence in negative results from DNT studies.

Animals↗