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T S Fletcher

Publications and source records attributed to T S Fletcher.

9 recordsLinked to original sources
PubMed1994

Modulation of intrinsic in vitro resistance to carboplatin by edatrexate in the A549 human nonsmall cell lung cancer cell line.

Edatrexate (10-ethyl-deazaaminopterin) is a methotrexate analog that has been shown to have greater antitumor activity and improved therapeutic index compared to its parent compound in preclinical systems. We have evaluated the ability of edatrexate to modulate the intrinsic resistance of the lung adenocarcinoma A549 cell line to carboplatin. Concentration effects, exposure time and schedule dependence were assessed. Modulation of resistance was observed with edatrexate treatment (0.2 microM for 1 h) prior to carboplatin. The concentrations of carboplatin to achieve IC50 at the 1-, 3-, and 24-h IC50 were decreased by a mean of 16.8 times (12.2-22.2) with edatrexate preexposure. In contrast, there was little modulation observed of carboplatin resistance when carboplatin was administered prior to edatrexate. In addition, schedule dependency experiments were performed using the method described by Chou and Talalay, in which the ratio of carboplatin to edatrexate was constant or nonconstant, and both the potency of effects and the shapes of the concentration-effect curves were taken into account in a computerized analysis. These experiments also demonstrated schedule dependency. Although both treatments resulted in a reduced IC50 vs. carboplatin alone, the reduction was much greater when edatrexate was added first (12.59 vs. 2.59 times). We conclude that the combination of edatrexate and carboplatin demonstrates schedule-dependent modulation of intrinsic carboplatin resistance in this in vitro model at clinically achievable edatrexate plasma levels (0.01 to 10 microM). The greatest modulatory synergism was observed in the setting of edatrexate treatment before carboplatin. Our findings suggest a potentially useful schedule when combining edatrexate and carboplatin for the treatment of malignant disease.

Aminopterin↗
PubMed1992

DNA sequence of the yeast transketolase gene.

Transketolase (EC 2.2.1.1) is the enzyme that, together with aldolase, forms a reversible link between the glycolytic and pentose phosphate pathways. We have cloned and sequenced the transketolase gene from yeast (Saccharomyces cerevisiae). This is the first transketolase gene of the pentose phosphate shunt to be sequenced from any source. The molecular mass of the proposed translated protein is 73,976 daltons, in good agreement with the observed molecular mass of about 75,000 daltons. The 5'-nontranslated region of the gene is similar to other yeast genes. There is no evidence of 5'-splice junctions or branch points in the sequence. The 3'-nontranslated region contains the polyadenylation signal (AATAAA), 80 base pairs downstream from the termination codon. A high degree of homology is found between yeast transketolase and dihydroxyacetone synthase (formaldehyde transketolase) from the yeast Hansenula polymorpha. The overall sequence identity between these two proteins is 37%, with four regions of much greater similarity. The regions from amino acid residues 98-131, 157-182, 410-433, and 474-489 have sequence identities of 74%, 66%, 83%, and 82%, respectively. One of these regions (157-182) includes a possible thiamin pyrophosphate (TPP) binding domain, and another (410-433) may contain the catalytic domain.

Aldehyde-Ketone Transferases↗
PubMed1987

Primary structure of human pancreatic elastase 2 determined by sequence analysis of the cloned mRNA.

A cDNA encoding elastase 2 has been cloned from a human pancreatic cDNA library. The cDNA contains a translation initiation site and a poly(A) recognition site and encodes a protein of 269 amino acids, including a proposed 16-residue signal peptide. The amino acid sequence of the deduced mature protein contains a 12-residue activation peptide containing a cysteine at residue 1 similar to that of chymotrypsin. The proposed active enzyme contains all of the characteristic active-site amino acids, including His-57, Asp-102, and Ser-195. The S1 binding pocket is bounded by Gly-216 and Ser-226, making this pocket intermediate in size between chymotrypsins and elastase 1 or protease E, consistent with the substrate specificity of elastase 2 for long-chain aliphatic or aromatic amino acids. Computer modeling studies using the amino acid sequence of elastase 2 superimposed on the X-ray structure of porcine elastase 1 suggest that a change of Gln-192 in elastase 1 to Asn-192 in elastase 2 may account for the lower catalytic efficiency of the latter enzyme. In addition, modeling studies have been conducted to attempt to identify basic amino acids in elastases which are absent in chymotrypsins, and which could account for the specific property of elastolysis. Several basic residues appear to be near the ends of the extended binding pocket of elastases which might serve to anchor the enzyme to the elastin substrate. These studies indicate that elastases 2 and elastase 1 both contain an Arg-65A as well as a basic dipeptide at 223/224 which is not present in chymotrypsins.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1987

Primary structure of human pancreatic protease E determined by sequence analysis of the cloned mRNA.

Although protease E was isolated from human pancreas over 10 years ago [Mallory, P. A., & Travis, J. (1975) Biochemistry 14, 722-729], its amino acid sequence and relationship to the elastases have not been established. We report the isolation of a cDNA clone for human pancreatic protease E and determination of the nucleic acid sequence coding for the protein. The deduced amino acid sequence contains all of the features common to serine proteases. The substrate binding region is highly homologous to those of porcine and rat elastases 1, explaining the similar specificity for alanine reported for protease E and these elastases. However, the amino acid sequence outside the substrate binding region is less than 50% conserved, and there is a striking difference in the overall net charge for protease E (6-) and elastases 1 (8+). These findings confirm that protease E is a new member of the serine protease family. We have attempted to identify amino acid residues important for the interaction between elastases and elastin by examining the amino acid sequence differences between elastases and protease E. In addition to the large number of surface charge changes which are outside the substrate binding region, there are several changes which might be crucial for elastolysis: Leu-73/Arg-73; Arg-217A/Ala-217A; Arg-65A/Gln-65A; and the presence of two new cysteine residues (Cys-98 and Cys-99B) which computer modeling studies predict could form a new disulfide bond, not previously observed for serine proteases. We also present evidence which suggests that human pancreas does not synthesize a basic, alanine-specific elastase similar to porcine elastase 1.

Amino Acid Sequence↗
PubMed1987

Isolation and characterization of a cDNA encoding rat cationic trypsinogen.

A cDNA encoding rat cationic trypsinogen has been isolated by immunoscreening from a rat pancreas cDNA library. The protein encoded by this cDNA is highly basic and contains all of the structural features observed in trypsinogens. The amino acid sequence of rat cationic trypsinogen is 75% and 77% homologous to the two anionic rat trypsinogens. The homology of rat cationic trypsinogen to these anionic trypsinogens is lower than its homology to other mammalian cationic trypsinogens, suggesting that anionic and cationic trypsins probably diverged prior to the divergence of rodents and ungulates. The most unusual feature of this trypsinogen is the presence of an activation peptide containing five aspartic acid residues, in contrast to all other reported trypsinogen activation peptides which contain four acidic amino acid residues. Comparisons of cationic and anionic trypsins reveal that the majority of the charge changes occur in the C-terminal portion of the protein, which forms the substrate binding site. Several regions of conserved charge differences between cationic and anionic trypsins have been identified in this region, which may influence the rate of hydrolysis of protein substrates.

Amino Acid Sequence↗
PubMed1986

Immunoenzymometric determination of trypsin/alpha 1-protease inhibitor complex in plasma of rats with experimental pancreatitis.

The currently available radioimmunoassays of trypsin measure total immunoreactive trypsin (EC 3.1.1.7), which includes both trypsinogen and alpha 1-protease inhibitor-bound trypsin. Hitherto, the only way to differentiate these two forms of trypsin has been to fractionate them on a gel-filtration column. We describe here a solid-phase immunoenzymometric assay that rapidly measures the amount of cationic trypsin bound to alpha 1-protease inhibitor in the plasma of rats with experimental pancreatitis. The assay specifically measures this complex within the range from 0.2 to 5.0 ng without interference by high concentrations of free alpha 1-protease inhibitor. The high correlation (r = 0.985) of the values obtained by size fractionation and by this assay demonstrates the accuracy of the assay, which is the first single-tube method for determining this form of activated cationic trypsin in plasma.

Animals↗
PubMed1985

Radioimmunoassay of active pancreatic enzymes in sera from patients with acute pancreatitis. I. Active carboxypeptidase B.

Previous studies have suggested that measurement of active enzymes in relation to proenzymes in serum of patients with pancreatitis may reflect the degree of zymogen activation in the gland. Here we describe the first single-tube assay for an active form of a pancreatic enzyme that is ordinarily synthesized as a proenzyme. Human procarboxypeptidase B, which we purified to near homogeneity, is approximately 13 000 Da larger than the active enzyme (EC 3.4.17.2). Antibodies specific for active carboxypeptidase B were obtained by affinity chromatography of anti-carboxypeptidase B antisera on a gel containing procarboxypeptidase B, then used to develop a single-tube radioimmunoassay for measuring active carboxypeptidase B in serum. Using this assay, we were able to detect, for the first time, active carboxypeptidase B in sera from patients with acute pancreatitis. Preliminary data show a correlation between the serum concentrations of active carboxypeptidase B and those of active trypsin complexed with serum inhibitors, but no correlation with serum amylase values.

Acute Disease↗
PubMed1978

Structural analysis of the ADHS electromorph of Drosophila melanogaster.

Population geneticists have often determined the fitness differences that account for the dynamics of naturally occurring genetic polymorphisms. However, to understand causal aspects of evolutionary processes requires, in addition, investigation of the physiological and molecular structural differences underlying adaptively significant genetic polymorphisms. The characteristics of the alcohol dehydrogenase gene--enzyme system in Drosophila melanogaster make it well suited for this kind of study. Natural populations of this species are polymorphic for two electrophoretically detectable variants, ADHF and ADHS, of the enzyme. Structural studies reported here reveal that the two variants differ by (at least) a single amino acid replacement, threonine in ADHF for lysine in ADHS.

Alcohol Oxidoreductases↗