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Biomedical subjects

J M Becker

Publications and source records attributed to J M Becker.

At least 217 records · Page 12Linked to original sources
PubMed1981

Synthesis of the dodecapeptide-alpha mating factor of Saccharomyces cerevisiae.

The synthesis of His-Trp-Leu-Gln-Leu-Lys-Pro-Gly-Gln-Pro-Met-Tyr, the dodecapeptide alpha-mating factor from Saccharomyces cerevisiae, and its Ala2- and Cha2-(beta-cyclohexylalanine) analogs are reported. Peptides were synthesized in solution using a combination of mixed anhydride and 1-hydroxybenzotriazole accelerated active ester coupling procedures. Dilute methanesulfonic acid (0.1-0.2 M) in methylene chloride-formic acid solution was employed to specifically remove the tert.-butoxycarbonyl group in the presence of the benzyloxycarbonyl group. Free peptides were obtained using catalytic transfer hydrogenation with formic acid as the hydrogen donor followed by mild acidolysis with trifluoroacetic acid. The alpha-factor and the Cha2-analog exhibited almost equal ability to cause "shmooing" of a-mating types of S. cerevisiae whereas the Ala2-analog exhibited no activity in this assay. These results differ with structure-activity studies reported on the tridecapeptide alpha-factor.

Amino Acid Sequence↗
PubMed1981

Myoelectric control of gastrointestinal and biliary motility: a review.

The movement of ingested food and secretions through the gastrointestinal and its appendages depends on a highly integrated and coordinated response of the smooth muscle contained within the wall of the gut. This review will consider, in detail, the various myogenic factors that contribute to the usual aboral propulsion of the gastrointestinal contents. The role of myoelectrical complexes as represented by slow waves and spike potentials are emphasized, for they appear to play a central role in the initiation of sphincter function and gastrointestinal peristalsis. The myoelectric control of the sphincter of Oddi is discussed in relationship to gastroduodenal motility, since disturbances in this finely modulated sphincter may lead to biliary-pancreatic dysfunction and symptoms of upper gastrointestinal disease.

Animals↗
PubMed1980

Amino acid uptake by Saccharomyces cerevisiae plasma membrane vesicles.

A procedure is described which allows for the efficient separation of Saccharomyces cerevisiae plasma membranes from other cellular membranes by discontinuous sucrose density gradient centrifugation. After vesiculization in an osmotic stabilization buffer the plasma membrane vesicles retain the ability to transport amino acids. Amino acid uptake was affected by the proton gradient dissipator m-chlorocarbonylcyanide phenylhydrazone and was dependent, in some cases, on the presence of sodium ion.

Amino Acids↗
PubMed1980

Tubular duplication with autonomous blood supply: resection with preservation of adjacent bowel.

This 10-mo-old patient represents an unusual small bowel duplication in that: (1) the duplication involved almost the entire small intestine; (2) the technetium scan was diagnostic; and (3) the duplication was resected, leaving the majority of normal bowel intact. Bremer, in his original discussion of the embryology of intestinal duplications, hypothesized the situation that was found in this patient, i.e., separate blood supplies, which, at first glance, appear to be contained within a single mesentery. This anatomical arrangement permitted the duplication to be resected, leaving the adherent normal small intestine.

Humans↗
PubMed1980

Endorectal "pull-through" without preliminary colostomy in neonates with Hirschsprung's disease.

The diagnosis of Hirschsprung's disease in the newborn does not mandate the performance of a preliminary colostomy. Enterocolitis can be adequately and safely treated by a precise regimen of colonic irrigations. The endo-rectal "pull-through" procedure is safe and effective when performed in the neo-natal period. Long-term follow-up is necessary to evaluate possible late complications.

Colon↗
PubMed1980

Anticandidal activity of pyrimidine-peptide conjugates.

The ability of conjugates of peptides and 5-fluorocytosine or 5-fluoroorotic acid to enter Candida albicans was investigated. A number of conjugates of 5-fluoroorotic acid and peptides were synthesized using 1-(ethoxy-carbonyl)-2-ethoxy-1,2-dihydroquinoline as the coupling agent. Orotyl-L-leucyl-L-leucine, 5-fluoro-4-(N-succinamoyl-L-alanyl-L-leucine)-2(1H)-pyrimidinone [a 5-fluorocytosine derivative], and 5-fluoroorotyl-L-leucyl-L-leucine all inhibited the uptake of trimethionine into C. albicans WD 18-4. Inhibition by 5-fluoroorotyl-L-leucyl-L-leucine was competitive as judged using double-reciprocal plots. Evaluation of minimum inhibitory concentrations of peptide-5-fluorocytosine conjugates suggest that these conjugates enter C. albicans in the intact form. These results provide the first experimental evidence that peptides can carry pyrimidines into a eukaryote.

Antifungal Agents↗
PubMed1980

Separation of peptide transport and hydrolysis in trimethionine uptake by Saccharomyces cerevisiae.

Intact cells of Saccharomyces cerevisiae 139 hydrolyzed amino acid-p-nitroanilide by an activity similar to that of aminopeptidase II, as well-characterized external peptidase in yeast. In contrast, trimethionine, a model peptide used in transport assays, was not hydrolyzed by this aminopeptidase II-like activity, and the peptidase activity toward this substrate was localized in the soluble fraction of the yeast. We conclude that this tripeptide is taken up by S. cerevisiae intact and rapidly hydrolyzed inside the cell.

Amino Acids↗
PubMed1979

Anticandidal activity of 5-fluorocytosine-peptide conjugates.

An approach to the development of new anticandidal drugs is described that employs peptides as carriers of toxic agents into cells. 5-Flurorcytosine (5-FC) was chosen as a toxic agent with which to prepare 5-FC-peptide conjugates as models to test the carrier proposal. Model compounds were synthesized and then tested for antiyeast activity against S. Cerevisiae 9763, C. albicans 1-V, C. albicans WD 18-4, and C. Krusei 1-T. The 5-FC derivatives showed antiyeast activity comparable to 5-FC in all strains except C. krusei 1-T, in which case the compounds were less active. The solution stabilities of 5-FC conjugates at 37 degrees C were tested in the same growth medium used for susceptibility testing. The results indicated a range of stabilities where the half-life (t1/2) = 0.3--17.6 h. These results and those obtained in the susceptibility testing suggest extracellular hydrolysis and indicate that the type of linkage used to conjugate 5-FC to peptides will not provide appropriate compounds to evaluate the peptide-carrier concept.

Antifungal Agents↗
PubMed1979

Peptide transport in Candida albicans.

The tripeptide L-methionyl-L-methionyl-L-[METHYL-14C]methionine was taken up into Candida albicans by a saturable system with a pH optimum of 3.5, a temperature optimum of 37 degrees C and an apparent Km of 3.3 x 10(-5) M. Metabolic inhibitors such as sodium azide and dinitrophenol completely prevented uptake. Neither methionine nor dimethionine effectively competed with trimethionine uptake. (Leu)3, Gly-Met-Gly, acetyl-(Met)3, D-Met-L-Met-L-Met and Met-Met-Ile effectively competed with (Met)3 uptake, whereas (Lys)3, L-Met-L-Met-D-Met, D-Met-D-Met-D-Met, (Met)3 methyl ester and (Ala)3 did not. Trimethionine was rapidly hydrolysed by a peptidase after entry into the cell.

Antimetabolites↗
PubMed1979

Peptidase activities in Saccharomyces cerevisiae.

At least four distinct aminopeptidase activities and a single dipeptidase activity were found in cell extracts of a leucine-lysine auxotroph of Saccharomyces cerevisiae. The assay for peptidase activity involved polyacrylamide gel electrophoresis followed by an enzyme-coupled activity staining procedure. The aminopeptidases had largely overlapping specificities but could be distinguished from one another by their electrophoretic mobilities and activities toward different peptide substrates. Substrates tested included both free and blocked di- and tripeptides and amino acid derivatives.

Amino Acids↗
PubMed1979

A model of biliary pancreatic reflux.

A primate model for the study of biliary pancreatic reflux under relatively physiological conditions is described. Cannulas were inserted into the gallbladder and the common bile duct of rhesus monkeys, and a pedicled segment of small bowel was used to create a pancreaticocutaneous fistula after resection of the spleen and pancreatic tail. Following recovery, Hypaque was instilled into the gallbladder with maintenance of common duct pressure within a normal range. The pancreatic duct was visualized in 21 of 34 radiographic studies (19 monkeys). Small amounts of iodine were detected in the fistula effluent of nine of 11 animals that refluxed radiologically. Radioactive polyethylene glycol (PEG-C14) was instilled into the gallbladder and pancreatic fistula drainage sampled by aspiration (26 studies, four monkeys). When compared to controls without PEG instillation (six studies, four monkeys), there was a significant rise in fistula counts beginning 50 minutes after injection and peaking at 180 minutes. In a second series of studies, pancreatic fistula aspiration was replaced by a flush technique using a triple-lumen cannula which allowed constant monitoring and control of fistula pressure. A statistically significant rise and fall of radioactivity after PEG introduction again was demonstrated. These data demonstrate taht biliary pancreatic reflux can occur and be quantitated under these experimental conditions.

Animals↗