Effects of the transciption inhibitory protein, TF1, on phage SP01 promoter complex formation and stability.

The uptake of a homologous single-stranded fragment by superhelical DNA produces a complex that contains a stable displacement loop. When the circular DNA was relaxed by the random action of pancreatic DNAase, complexes dissociated by a process which requires that the single-stranded arm of the D-loop be intact. We attribute the dissociation to branch migration, the exchange of like strands at a branch point. The kinetics of dissociation were biphasic. A fraction of the nicked complexes dissociated in a few seconds, the rest dissociated much more slowly. The fraction of molecules that dissociated slowly was directly related to the length of the third strand, and inversely related to temperature. Salt also inhibited dissociation. Under physiological conditions, 37 °C and 0.15 m-NaCl, more than half of complexes containing a third strand of 1000-nucleotide residues survived for at least one minute. These observations provide a guide to handling certain natural or synthetic branched derivatives of DNA. Analyzing our data by the method of Thompson et al. (1976), we have estimated that the time for the exchange of one nucleotide for another at a single-stranded branch is 12 microseconds; but the calculated value depends strongly upon the assumption that single-strand branch migration occurs by a random walk.     

CARBOHYDRATE AND ENERGY METABOLISM IN PERINATAL RAT BRAIN: RELATION TO SURVIVAL IN ANOXIA

The ability of rats of different ages to survive exposure to anoxia was correlated with rates of high energy phosphate consumption (metabolic rates) of the fore-brain. Fetal rats at term, delivered by hysterotomy following maternal decapitation, survived in nitrogen at 37°C twice as long as 1-day-old neo-nates, 5 times longer than 7-day-old rats, and 45 times longer than adults. During ischemia induced by decapitation, the cerebral concentrations of the labile energy reserves (ATP, ADP, P-creatine, glucose and glycogen) and of lactate were determined in fetuses, 1- and 7-day post-natal animals. From the changes, the cerebral energy use rates were calculated to be 1·57 mmol/kg/min in fetuses, 1·33 mmol/kg/min in 1-day-olds and 2·58 mmol/kg/min in 7-day-olds. Maximal rates of lactate accumulation during ischemia, as a measure of glycolytic capacity, were comparable in fetuses and neonates, but were about twice as great in 7-day-old rats. It is concluded that in post-natal animals survival in anoxia and cerebral energy consumption are inversely, and nearly quantitatively, related. However, the reduced cerebral energy requirement cannot entirely account for the greater anoxic resistance of fetuses.     

Submarine foraging behavior of alcids in an artificial environment

We used an artificial environment at Sea World, Inc, San Diego, to study underwater foraging behavior of alcids. Larger birds dove longer and had greater wingbeat frequencies. The pigeon guillemot Cepphus columba was the only species to use both feet and wings for propulsion; all others used just wings. Aggressive interactions underwater were common. Competition among alcids in the wild may occur primarily underwater, and artificial environments may be the best means to study such interactions.     

Suppression of postprandial glucose, insulin, C-peptide, and glucose-dependent insulinotropic peptide (GIP) in man by oral administration of a prostaglandin analogue (enprostil)

Enprostil, a long-acting, orally active dehydroprostaglandin E2 with cytoprotective and gastric antisecretory properties, is a potent inhibitor of meal-stimulated gastrin release. Recent data have suggested suppression of additional other gastrointestinal peptide hormones following single doses of enprostil. The current investigation was conducted to further clarify the effects of enprostil administration on gastrointestinal hormones and glucose metabolism under physiologic conditions and to determine whether these effects were present following multiple doses of the agent. Enprostil 70 mcg/d and its placebo were each administered for 7 1/2 days to eight normal male subjects in a study of crossover design, each treatment period lasting 7 1/2 days and separated by a 7 day washout period. Subjects received a test meal on days 1 and 8 and an oral glucose challenge on day 3 of each treatment period following enprostil or its placebo. Following the test meal, there was a delay and suppression of the maximum measured serum glucose levels. Mean overall peak glucose concentrations were lower during the enprostil phase compared to placebo (112 vs. 121 mg/dd, P = 0.025) with a trend toward delay in the time to achievement of peak glucose concentrations. Mean overall peak levels for insulin, C-peptide, and glucose-dependent insulinotropic peptide (GIP) were significantly suppressed by 36%, 16% and 60%, respectively by enprostil when compared to placebo. The overall integrated postprandial responses for insulin, C-peptide, and GIP were significantly reduced by 42%, 39% and 90%, respectively while that for glucose above baseline was reduced by 44% (P = 0.098). Similar effects were present following the oral glucose challenge.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cholera toxin A subunit: functional sites correlated with regions of secondary structure

The A subunit of cholera toxin contains the ADP-ribosyltransferase activity in its major constituent polypeptide A1 (Mr 23,000) which is responsible for the elevation of cAMP typically observed with most mammalian cell types after exposure to the toxin. The primary structure of the A subunit, recently established by sequence analyses, is presented and used as the basis for the secondary structure prediction according to the method of Chou and Fasman. The results indicated the presence of 27% alpha-helix, 25% beta-structure, 12% beta-turn, and 36% random coil. The majority of the beta-structure consisted of six strands located in the NH2-terminal portion of the molecule (residues 33-106) covering one-half of the region corresponding to the A1 polypeptide portion. The beta-sheet domain led immediately into the active site region characterized by the alternating structures of beta-pleated sheet and alpha-helix (residues 95-140) similar to that reported for other NAD+ binding proteins. The presence of this structural feature in the region was confirmed by the use of another predictive method (J. Garnier et al., J. Mol. Biol. 1978, 120, 97-120). In addition, two regions (residues 14-18 and 200-214), previously identified to contain binding sites for the B subunit as evidenced by chemical modification and monoclonal antibody studies, were found to be in alpha-helix configuration.