PubMed Health⌕ Search

Biomedical subjects

J M Becker

Publications and source records attributed to J M Becker.

At least 19 recordsLinked to original sources
PubMed1995

Attenuated virulence of chitin-deficient mutants of Candida albicans.

We have analyzed the role of chitin, a cell-wall polysaccharide, in the virulence of Candida albicans. Mutants with a 5-fold reduction in chitin were obtained in two ways: (i) by selecting mutants resistant to Calcofluor, a fluorescent dye that binds to chitin and inhibits growth, and (ii) by disrupting CHS3, the C. albicans homolog of CSD2/CAL1/DIT101/KT12, a Saccharomyces cerevisiae gene required for synthesis of approximately 90% of the cell-wall chitin. Chitin-deficient mutants have no obvious alterations in growth rate, sugar assimilation, chlamydospore formation, or germ-tube formation in various media. When growing vegetatively in liquid media, the mutants tend to clump and display minor changes in morphology. Staining of cells with the fluorescent dye Calcofluor indicates that CHS3 is required for synthesis of the chitin rings found on the surface of yeast cells but not formation of septa in either yeast cells or germ tubes. Despite their relatively normal growth, the mutants are significantly less virulent than the parental strain in both immunocompetent and immunosuppressed mice; at 13 days after infection, survival was 95% in immunocompetent mice that received chs3/chs3 cells and 10% in immunocompetent mice that received an equal dose of chs3/CHS3 cells. Chitin-deficient strains can colonize the organs of infected mice, suggesting that the reduced virulence of the mutants is not due to accelerated clearing.

Animals↗
PubMed1995

The PTR family: a new group of peptide transporters.

The transport of peptides into cells is a well-documented biological phenomenon which is accomplished by specific, energy-dependent transporters found in a number of organisms as diverse as bacteria and humans. Until recently, the majority of peptide transporters cloned and characterized were found to be proteins of the ATP-binding cassette (ABC) family. We report the identification of a new family of peptide transporters, which we call the PTR family. This group of proteins, distinct from the ABC-type peptide transporters, was uncovered by sequence analyses of a number of recently discovered peptide transport proteins. Alignment of these proteins demonstrated a high number of identical and similar residues and identified conserved glycosylation and phosphorylation sites, as well as a structural motif unique to this group of proteins. Cluster analysis among the proteins indicated these sequences were indeed related and could be further divided into two subfamilies. A phylogenetic analysis of these new peptide transport sequences, compared to over 50 other peptide and membrane-bound transporters, showed that these proteins comprise a distinct, separate group of proteins.

Amino Acid Sequence↗
PubMed1992

Antagonistic and synergistic peptide analogues of the tridecapeptide mating pheromone of Saccharomyces cerevisiae.

Biologically inactive, truncated analogues of the Saccharomyces cerevisiae alpha-mating factor (WHWLQLKPGQPMY) either antagonized or synergized the activity of the native pheromone. An amino-terminal truncated pheromone [WLQLKPGQP(Nle)Y] had no activity by itself, but the analogue acted as an antagonist by competing with binding and activity of the mating factor. In contrast, a carboxyl-terminal truncated pheromone [WHWLQLKPGQP] was not active by itself nor did the peptide compete with alpha-factor for binding to the alpha-factor receptor, but it acted as a synergist by causing a marked increase in the activity of alpha-factor. The observation that residues near the amino terminus may be involved in signal transduction whereas those near the carboxyl terminus influence binding allows us to separate binding and signal transduction in the yeast pheromone response pathway. If found for other hormone-receptor systems, synergists may have potential as therapeutic compounds.

Amino Acid Sequence↗
PubMed1992

Studies on the yeast alpha-mating factor: a model for mammalian peptide hormones.

Small peptides initiate sexual conjugation in the yeast Saccharomyces cerevisiae and this phenomenon is an ideal paradigm for studying the mode of action of mammalian peptide hormones. 1H-nmr spectroscopy was used to examine the conformation of linear and cyclic analogues of the alpha-factor (WHWLQLKPGQPMY) in aqueous solution. In all cases peptides that exhibit nmr parameters expected for a type II beta-turn have higher biological activities than those that do not appear to assume this conformation. Based on a simple model for the interaction of the pheromone with its receptor, we prepared fragments of the alpha-factor. Several of these fragments either antagonize or potentiate the activity of the alpha-factor. The latter represent the first example of peptide fragments that synergize the activity of the parent pheromone.

Amino Acid Sequence↗
PubMed1992

The lysine analog L-oxalysine is an inhibitor of RNA synthesis.

1. The lysine analog L-4-oxalysine was found to be a potent inhibitor of RNA synthesis in Candida albicans. 2. The compound was a weak inhibitor of protein synthesis and DNA synthesis was not affected. 3. The inhibition of RNA synthesis was reversed by L-lysine but not D-lysine. 4. The decrease in the level of newly synthesized RNA in cells treated with L-oxalysine was due to inhibition of de novo synthesis rather than to degradation of RNA.

Amino Acids↗
PubMed1992

Superior results of ileoanal pull through (IAPT) in polyposis coli vs ulcerative colitis patients.

Colectomy, mucosal proctectomy, and ileoanal pull through (IAPT) have replaced proctocolectomy as the operation of choice in most patients with the colorectal mucosal diseases ulcerative colitis and polyposis coli. This study was conducted to determine whether there is any difference in postoperative morbidity and long-term functional results when IAPT is performed for polyposis coli than when it is performed for ulcerative colitis patients. Between 1982 and 1989, 277 IAPT procedures were performed at the University of Utah Medical Center, 239 for ulcerative colitis and 38 for polyposis coli syndromes. A prospective study compared polyposis and colitis patients after IAPT with regards to age, family history, preoperative findings, operative findings, postoperative complications, and long-term complications. Functional results were compared including day and night stool frequency, incidence of nighttime incontinence, and incidence of pouchitis. The incidence of postoperative complications was lower in the polyposis group than in the colitis group, but the numbers were low enough in both diseases that significant differences were not detected. However, the incidence of pouchitis (0% vs 19%), day (4.2 vs 6.0) and night (0.4 vs 0.9) stool frequency, and nighttime incontinence (5% vs 25%) was significantly lower in the polyposis group when compared to the colitis group. We conclude that IAPT performed for polyposis conditions is associated with superior results when compared with results from patients who undergo the procedure for ulcerative colitis.

Adenomatous Polyposis Coli↗
PubMed1992

A simplified technique for open laparoscopy using disposable trocars.

An easily accomplished method for performing open laparoscopy with disposable trocars is presented. This technique provides for safe entry into the peritoneum and subsequently facilitates removal of the gallbladder and any larger stones at the completion of the procedure.

Cholecystectomy, Laparoscopic↗
PubMed1992

Toxicity of oxalysine and oxalysine-containing peptides against Candida albicans: regulation of peptide transport by amino acids.

A lysine antimetabolite, L-4-oxalysine [H2NCH2CH2OCH2CH(NH2)COOH], and oxalysine-containing di-, tri-, tetra- and pentapeptides inhibited growth of Candida albicans H317. Micromolar amounts of amino acids were found to overcome ammonium repression of the di- and tripeptide transport system(s) in strain H317. Several amino acids increased the toxicity of oxalysine-containing di- and tripeptides for C. albicans with little or no increase in toxicity of oxalysine or oxalysine-containing tetra- and pentapeptides. L-Lysine completely reversed the toxicity of oxalysine by competing with the transport of oxalysine into the cells. In contrast, L-lysine increased the toxicity of oxalysine-containing di- and tripeptides, but had no effect on the toxicity of oxalysine-containing tetra- and pentapeptides. Incubation of cells with L-lysine for 4 h resulted in a 15-fold increase in the rate of transport of radiolabelled dileucine, indicating that increased sensitivity of C. albicans to some toxic peptides in the presence of L-lysine may be attributed to an increased rate of transport of these peptides. Our results indicate that the dipeptide and tripeptide transport system(s) of C. albicans are regulated by micromolar amounts of amino acids in a similar fashion to the regulation of peptide transport in Saccharomyces cerevisiae and that multiple peptide transport systems differentially regulated by various nitrogen sources and amino acids exist in C. albicans.

Amino Acid Sequence↗
PubMed1992

Preservation and propagation of cyclic myoelectric activity after feeding in rat small intestine.

The cyclic nature and distal propagation of the fasting migrating motor complex (MMC) of the small intestine have been well described. The fate of the MMC after feeding, however, has not been elucidated. We used time series analysis with fast Fourier transforms (FFT) to study myoelectric cycling before and after feeding. Ten rats were chronically prepared with bipolar electrodes secured to the duodenum and proximal jejunum. Spikeburst frequency was recorded before and after feeding simple nutrients. During fasting, cyclic activity occurred at the MMC frequency. Although after feeding this periodicity appeared disrupted, FFT analysis showed persistent cycling at the fasted (MMC) rate. Digital filtering of data at the MMC frequency isolated cycling from background noise during both fasted and fed states and showed a depression in the amplitude of the waveform after feeding. Root-mean-square analysis of the waveform confirmed statistically significant depression of amplitude by 47-57%. The waveform propagated from the duodenum to the jejunum during both the fasted and fed state at an unchanged rate. We conclude that factors controlling myoelectric cycling during the fasted state persist after feeding, allowing continued net abroad propulsion of food.

Administration, Oral↗
PubMed1991

The conformation of a-factor is not influenced by the S-prenylation of Cys12.

Two-Dimensional NMR was used to examine the solution conformation of the lipopeptide a-factor, YIIKGVFWDPAC (S-farnesyl) OCH3, from the yeast Saccharomyces cerevisiae and five analogues containing various S-alkylated cysteines in DMSO-d6. NOESY data, NH temperature coefficients, and 3J alpha NH coupling constants indicate that the a-factor is a predominantly unstructured peptide in DMSO. Similar results were obtained for the other peptides indicating that S-prenylation of Cys12 does not affect the conformation of these peptides.

Acylation↗
PubMed1991

Mass spectrometric signature of S-prenylated cysteine peptides.

The fast atom bombardment mass spectra of peptides containing S-prenylated cysteine display signature fragmentations characteristic of this modified amino acid. The fragmentation is independent of the nature of the cysteine carbonyl substituent, easily differentiates prenyl from nonprenyl alkylation, and readily identifies the oligomer count of the prenyl. This screening method, which requires little time, effort, or material (compared with previous analysis methods based on chemical degradation), greatly facilitates the identification of these prenylated proteins.

Amino Acid Sequence↗
PubMed1991

Isolation and characterization of S. cerevisiae mutants deficient in amino acid-inducible peptide transport.

The transport of small peptides into the yeast Saccharomyces cerevisiae is subject to complex regulatory control. In an effort to determine the number, and to address the function, of the components involved in peptide transport and its regulation, spontaneous mutants resistant to toxic di- and tripeptides were isolated under inducing conditions. Twenty-four mutant strains were characterized in detail and fell into two phenotypic groups; one group deficient in amino acid-inducible peptide uptake, the other with a pleiotropic phenotype including a loss of peptide transport. Complementation analysis of recessive mutations in 12 of these strains defined three groups; ptr1 (nine strains), ptr2 (two strains), and ptr3 (one strain). Isolation and screening of 31 additional N-methyl-N-nitro-N-Nitrosoguanidine (MNNG)-induced, peptide transport-deficient mutants produced one ptr3 and 30 ptr2 strains: no additional complementation groups were detected. Uptake of radiolabeled dileucine was negligible in ptr1 and ptr2 strains and was reduced by 65% and 90% in the two ptr3 mutants, indicating that all strains were defective at the transport step. We conclude that the S. cerevisiae amino acid-inducible peptide transport system recognizes a broad spectrum of peptide substrates and involves at least three components. One gene, PTR3, may play an indirect or regulatory role since mutations in this gene cause a pleiotropic phenotype.

Amino Acids↗
PubMed1991

Laparoscopic cholecystectomy.

Laparoscopic cholecystectomy has emerged in the last 2 years as a unique procedure that offers the long-term advantages of open cholecystectomy without much of the short-term morbidity. Importantly, when compared with non-surgical approaches to symptomatic gallstones, it is suitable for virtually all patients rather than a highly-selected group as in the case of oral bile salt dissolution therapy or extracorporeal lithotripsy. Furthermore, it obviates the high recurrence rate seen with these techniques. Complications including bleeding and ductal injury appear to occur at a slightly higher rate than with traditional open cholecystectomy, but most surgeons who have had experience with the procedure predict that these complications will become rarer as more experience is gained. We may indeed be witnessing the first major successful challenge to traditional surgical management of symptomatic gallstone disease in 100 years.

Cholecystectomy↗
PubMed1991

Synthesis and biological evaluation of dipeptidyl and tripeptidyl polyoxin and nikkomycin analogues as anticandidal prodrugs.

Nine analogues (1-5, 9-12) of the peptidyl nucleoside antibiotics nikkomycin and polyoxin were synthesized and tested for their biological properties against different strains of the pathogenic yeast Candida albicans. The tripeptidyl series of analogues (1-5) was designed to behave as prodrugs, releasing a toxic moiety upon enzymatic hydrolysis inside the cell. The dipeptidyl series (9-12) was designed as double-targeted drugs, being themselves toxic and releasing a toxic amino acid upon hydrolysis. All the analogues were prepared by coupling suitably protected amino acid p-nitrophenyl esters to 1-(5'-amino-5'-deoxy-alpha-D-allofuranuronosyl)uracil (UPOC) or the corresponding polyoxins and nikkomycins, with subsequent removal of the protecting group. Improved coupling yields were observed when DMSO was used as the solvent. Products were purified with use of reversed-phase HPLC and, in one case, diastereomeric products (compound 11) were resolved by using this procedure. One of the tripeptidyl nikkomycins behaved as a prodrug but none of the compounds, as measured by in vitro testing, proved more effective than nikkomycin as an anticandidal agent.

Aminoglycosides↗
PubMed1991

Colectomy, mucosal proctectomy, and ileal pouch-anal anastomosis. A prospective trial of optimal antibiotic management.

The ideal prophylactic antibiotic regimen has not been established for patients undergoing colectomy, mucosal proctectomy, and endorectal ileoanal anastomosis, a prolonged operation frequently accompanied by abdominal and pelvic contamination and associated with an infection rate up to 20%. The aim of this study was to evaluate, in a prospective, randomized, double-blind fashion, the efficacy of a short perioperative course compared to an extended postoperative course of intravenous antibiotics (cefoxitin) in patients undergoing colectomy with ileoanal anastomosis. Forty patients with ulcerative colitis or familial polyposis coli received a mechanical and oral antibiotic bowel preparation and a standard three-dose perioperative course of intravenous cefoxitin. Patients then were randomized to receive intravenous cefoxitin, 1 g every 6 hours, or placebo for 5 days. No differences in overall postoperative morbidity were observed and neither group developed intra-abdominal, pelvic, or wound infections. It is concluded that a standard three-dose perioperative course of intravenous antibiotics provides adequate prophylaxis in the prevention of infectious complications in patients undergoing colectomy, mucosal proctectomy, and ileoanal anastomosis.

Adenomatous Polyposis Coli↗
PubMed1991

Synthesis of S-alkyl and C-terminal analogs of the Saccharomyces cerevisiae a-factor. Influence of temperature on the stability of Fmoc and OFm groups toward HF.

The a-mating factor of Saccharomyces cerevisiae Tyr-Ile-Ile-Lys-Gly-Val-Phe-Trp-Asp-Pro-Ala-Cys(farnesyl)OCH3, and 10 analogs modified at the cysteine side chain and/or the terminal carboxyl were synthesized using a combination of solid phase and solution phase methodologies. The strategy of synthesis involved the condensation of an amine terminal protected decapeptide with a carboxyl terminal S-alkylated dipeptide ester or amide using benzotriazol-l-yloxy-tris(methylamino)-phosphonium hexafluorophosphate as the coupling agent. The protected decapeptide was assembled on a PAM-resin using 9-fluorenylmethoxycarbonyl (Fmoc) for the protection of the Tyr alpha-amine and Lys epsilon-amine and 9-fluorenylmethyl ester (OFm) for the protection of the Asp beta-carboxyl. Premature loss of the OFm group from the HF cleavage was observed at 0-2 degrees, whereas no loss occurred when the cleavage reaction was conducted at -5 degrees. In contrast to these results, the OFm group in Asp(OFm) was partially removed by HF at -5 degrees and was completely stable to HF only at -20 degrees. The S-alkylated dipeptide esters were prepared, in yields from 64% to 88%, via thioalkylation of amine protected or unprotected dipeptide esters using potassium fluoride dihydrate as the base. The use of a tertiary amine as the base of thiohexadecanylation resulted in low reactivity.

Alkylation↗