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Biomedical subjects

M Southworth

Publications and source records attributed to M Southworth.

11 recordsLinked to original sources
PubMed1997

The Mycobacterium xenopi GyrA protein splicing element: characterization of a minimal intein.

The 198-amino-acid in-frame insertion in the gyrA gene of Mycobacterium xenopi is the smallest known naturally occurring active protein splicing element (intein). Comparison with other mycobacterial gyrA inteins suggests that the M. xenopi intein underwent a complex series of events including (i) removal of 222 amino acids that encompass most of the central intein domain, and (ii) addition of a linker of unrelated residues. This naturally occurring genetic rearrangement is a representative characteristic of the taxon. The deletion process removes the conserved motifs involved in homing endonuclease activity. The linker insertion represents a structural requirement, as its mutation resulted in failure to splice. The M. xenopi GyrA intein thus provides a paradigm for a minimal protein splicing element.

Amino Acid Sequence↗
PubMed1990

Colonoscopy in critically ill patients. What conditions call for it?

Indications for colonoscopy in the intensive care unit include acute lower intestinal bleeding, sigmoid volvulus, pseudo-obstruction of the colon, and suspicion of pseudomembranous colitis. Although the incidence of cardiorespiratory complications may be higher in these critically ill patients, the procedure can be done safely with proper attention to detail. Because of colonic dilatation, endoscopy can often be done without bowel preparation.

Colonic Diseases↗
PubMed1981

Absorption of volatile fatty acid, Na, and H2O by the colon of the dog.

Volatile fatty acid (VFA) concentrations were examined in the gastrointestinal tract of dogs 24 and 48 hours after a meal. Small concentrations of VFA were present in the stomach and small intestine. Large concentrations were present in the large intestine at both periods after the meal, but the total quantity was reduced markedly between 24 and 48 hours. Colonic absorption and transport of VFA also were examined with in vitro and in vivo perfusion procedures. Both demonstrate that VFA were rapidly absorbed and that the rate of absorption/cm2 of colonic mucosa ws equivalent to that measured in the pig. In vivo results showed that VFA and Na were absorbed at the same rate, and their absorption showed a parallel increase with a decrease in pH of the perfusate. Absorption of Na and VFA alone could account for osmotic absorption of H2O from the colon. Results indicated that although the total quantity of VFA absorbed by the colon of the dog would be nutritionally insignificant, their absorption is of major importance to normal colonic absorptive processes.

Animals↗
PubMed1975

Sites of organic acid production and pattern of digesta movement in the gastrointestinal tract of geese.

Sixteen geese were used to assess the movement of fluid and particulate digesta through their gastrointestinal tracts and to determine the diurnal variation in organic acid levels for the various segments of the tract. Fluid (polyethylene glycol and chronium-labeled ethylenediaminetetraacetic acid) and particulate markers (2 and 5 mm long) were administered with the meal. Animals were killed at given intervals after the administration of markers. The gastrointestinal tract was divided into nine segments for measurement of markers, pH, volatile fatty acids (VFA), and lactic acid contents. The data indicated a rapid evacuation of fluid marker from the foregut (crop, ventriculus, and proventriculus), while particulate markers were retained for extended periods of time. Retention of fluid marker was observed only within the cecum. Retrograde movement of particulate marker was demonstrated from the duodenum to ventriculus and proventriculus. Retrograde movement of fluid marker was observed from the cloaca to the colon, cecum, and distal third of the small intestine. However, particulate marker showed no retrograde movement in these segments of tract. Highest VFA levels were observed in the cecum. Retention of digesta and production of VFA within the colon were less than those noted for the dog, pig and pony. Lactic acid comprised less than 10% of the organic acids present in the gastrointestinal tract and were at their highest levels in the proximal and mid small intestine.

Animals↗
PubMed1975

Sites of organic acid production and pattern of digesta movement in the gastrointestinal tract of swine.

Twelve swine were used to assess the movement of fluid and particulate digesta through their gastrointestinal tracts and to determine the diurnal variations in organic acid levels for various segments of the tract. Animals were fed twice daily at 12-hour intervals. Fluid (polyethylene glycol and chromium-labeled ethylenediamine-tetraacetic acid) and particulate markers (2 mm OD, and 2 mm and 1 and 2 cm long) were administration of markers. The gastrointestinal tract was divided into 12 segments for measurements of markers, pH, volatile fatty acids (VFA), and lactic acid (LA) contents. The data indicated a rapid evacuation of the fluid and the smaller particles from the stomach and their relatively rapid passage through the small intestine and cecum. There was, however, prolonged retention of both fluid and particulate markers first in the ascending and then in the descending colon. Larger particles (2 cm) were retained in the stomach throughout much of the 60-hour experimental period. LA levels were observed 8 hours postfeeding. The highest levels of VFA in gastric contents averaged 20 mmoles/liter. Gastrointestinal pH values showed significant changes with time postfeeding only within the stomach, where they did not reflect the changes in LA of VFA concentrations. VFA constituted 92% of the organic acids present in the large intestine. Their concentrations varied markedly with time (150-230 mmoles/liter), but the VFA at all times constituted the major anions in the large intestinal contents. The results demonstrated that digesta can be retained for prolonged periods of time in that swine stomach and colon. The high concentrations of organic acids also indicated that substantial degrees of microbial digestion of carbohydrates occurred at both sites.

Animals↗
PubMed1975

Sites of organic acid production and absorption in gastrointestinal tract of the pig.

The relationship between diet, pH, and microbial digestion of carbohydrate was examined in 24 pigs fed either a conventional or a low-protein, high-cellulose experimental diet and sacrificed 2, 4, 8, or 12 h after a meal. In animals fed the control diet contents of the cranial half of the stomach demonstrated marked, cyclic fluctuations in pH and high concentrations of organic acids. Contents of the caudal (glandular) half were lower in both pH and organic acid concentration. Despite concentrations of volatile fatty acids (VFAs) as high as 250 meq/liter in the large intestine, the pH remained relatively neutral. The VFA levels remained relatively constant throughout the length of the colon. The VFA transport across isolated gastric and large intestinal mucosa also was examined. All four types of gastric mucosa absorbed and transported VFA at substantial rates. Mucosa of pig cecum and colon transported VFA at much greater rates than gastric mucosa and greater rates than previously determined in equine large intestinal mucosa or even bovine rumen epithelium. Comparison with results of earlier studies in the pony suggested that the higher concentration of VFA in the large intestinal contents of pigs was due to the more rapid rate of digesta passage rather than to less efficient absorption of fatty acids.

Animals↗
PubMedDate not supplied

Constitutive error-prone repair at sites of excision repair in Escherichia coli: a re-examination.

No evidence was found for production during incubation in chloramphenicol of a signal capable of inducing a rec-lex function (lysogenic induction) when protein synthesis was restored. The majority of UV-induced mutations to streptomycin resistance require lesions in the DNA and cannot be attributed to untargeted mutator activity. Therefore the loss of photoreversibility of these mutations occurring in the absence of protein synthesis and DNA replication cannot be attributed to the production of a signal for the induction of subsequent rec-lex dependent mutator activity. The simplest interpretation is that they arise as errors at excision sites by the operation of a constitutive pathway.

DNA Repair↗