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D M Webster

Publications and source records attributed to D M Webster.

33 records · Page 2Linked to original sources
PubMed1982

Disruption of conditioned taste aversion by the combined effects of LiCl and ECS.

Rats were taught a conditioned taste aversion by allowing them to drink sucrose (CS) for 5 min and 30 min later poisoning them with LiCl (UCS). Experimental animals were given ECS (80 mA for 250 msec) at 0, 15, 20, 25, 27.5, 30, 32.5, 35, 40, or 45 min after the CS. Only animals given ECS both within the CS-UCS interval and in close temporal proximity to the UCS (within 5 min) showed a significant, although limited, disruption of learning. At least two explanations are possible. The first is that apart from its toxicity, LiCl may also possess amnesic properties which interact with those of the ECS. Alternatively, ECS may have impaired the ability of the animals to fully experience the lithium-induced illness.

Animals↗
PubMed1982

Carboxymethylation of thiol groups in ovalbumin: implications for proteins that contain both thiol and disulfide groups.

The cysteine residues of hen ovalbumin were S-carboxymethylated with non-radioactive iodoacetic acid under various conditions by altering the pH at which the protein was denatured in 8 M urea, by using different molar ratios of non-radioactive iodoacetic acid to cysteine and by varying the time at which carboxymethylation was commenced after denaturing conditions had been applied. Under the various conditions, the thiol groups were carboxymethylated to different extents, the residual thiol groups being measured by reaction with 5,5'-dithiobis(2-nitrobenzoic acid) in the presence of sodium dodecyl sulfate. When ovalbumin is carboxymethylated in alkaline urea, it unfolds slowly and the carboxymethylation is incomplete even with 150-fold excess iodoacetic acid. The known rapid thiol-disulfide exchange that occurs at alkaline pH values makes this method of carboxymethylation unsuitable as a preliminary step for blocking the native cysteine residues of ovalbumin before reduction and labelling the thiol groups formed by reduction of the disulfide bonds. Titration of the thiol groups of ovalbumin in 6 M guanidine hydrochloride or 1% (w/v) sodium dodecyl sulfate at pH 8.2 with 5,5'-dithiobis(2-nitrobenzoic acid) is more rapid than in 8 M urea and these solvents would be preferable for studies of the disulfide-bonded sequences. Denaturation of ovalbumin in acidic 8 M urea is a very rapid process, and under mild acid conditions thiol-disulfide interchange is much slower. Subsequent carboxymethylation of the cysteine residues at alkaline pH with 150-fold excess iodoacetic acid results in complete carboxymethylation and the carboxymethylated ovalbumin can be reduced and labelled with radioactive iodoacetic acid with specific labelling of the half-cystine residues involved in the disulfide bond. The results are discussed in relation to the allocation of half-cystine residues in other protein systems that contain both thiol and disulfide groups.

Amino Acid Sequence↗
PubMed1981

Amino acid sequences containing cysteine or cystine residues in ovalbumin from eggs of the quail Coturnix coturnix japonica.

Ovalbumin isolated from eggs of the Japanese quail, C. c. japonica, was subjected to limited proteolysis by subtilisin to give plakalbumin and then fractionated on Sephadex G75 in acid-urea to give plakalbumin S-protein and S-peptide. The plakalbumin peptide was recovered, oxidized with performic acid, and the sequence of amino acids determined from the peptides formed by enzyme digestion. There were two cysteine residues in the 33-residue sequence. The ovalbumin was also oxidized with performic acid and digested with thermolysin and pepsin before isolating, from a sulfonated polystyrene column, the acidic cysteic acid peptides, as well as acetylated N-terminal peptides and phosphorylated peptides, and determining their amino acid sequence. Additional peptide sequences containing cysteine or half-cystine were characterized. Quail ovalbumin was reduced and carboxymethylated with [2-14C]iodoacetic acid. Peptides containing labelled S-carboxymethylcysteine residues were isolated from thermolytic digests of the carboxymethylated ovalbumin by paper ionophoresis and chromatography. Their amino acid sequence was determined and five different sequences involving labelled S-carboxymethylcysteine residues were established. The presence of two half-cystine residues and the location of the disulfide bond were shown by blocking the cysteine residues with non-radioactive iodoacetic acid, reducing the disulfide bond and labelling the half-cystine residues with [2-14C]iodoacetic acid. After thermolytic digestion of the protein, radioactive peptides were isolated by paper ionophoresis and chromatography. These studies have thus shown that quail ovalbumin contains one cystine residue and three cysteine residues, which is one residue of cysteine less than in ovalbumin from the hen (Gallus gallus domesticus). There is strong homology in the amino acid sequences of hen ovalbumin and quail ovalbumin determined in these investigations.

Amino Acid Sequence↗
PubMed1979

Disruption of taste aversion learning by pentylenetetrazol.

Rats were taught an aversion to a sucrose taste cue (CS) by pairing it with lithium chloride-induced toxicosis (UCS). The CS-UCS interval was 30 min. Animals were injected with pentylenetetrazol (PTZ) (50 mg/kg at 0, 15, 25, 28 or 30 min after the CS in an attempt to disrupt taste aversion learning. Only animals given PTZ 30 min after the CS (simultaneously with the UCS) showed a significant learning deficit. However, learning deficits were also observed in individual animals in groups given PTZ at 15, 25 and 28 min. As lithium salts may produce seizures and abnormal electroencephalographic activity, it is suggested that the neurophysiological consequences of PTZ administration may interact with those of LiCl, causing a greater amnesic effect than PTZ by itself. The resulting interference with the memory trace is probably affecting either the neural engram underlying the CS or the associative bond between the CS and UCS. Evidence was also found that PTZ could act as a UCS with which to establish a mild taste aversion.

Animals↗
PubMed1975

Mediodorsal nucleus and behavior regulation in the rat.

Twelve electrodes aimed at the mediodorsal thalamic nucleus were implanted in 6 rats. In 5 of these animals intracranial stimulation was effective in punishing a bar press response on a baseline schedule of water reinforcement. The sixth animal was not tested. In all 6 animals lesions produced through these electrodes disrupted response suppression to punishing electric shock superimposed on the same baseline. Those animals in which both parts of the mediodorsal thalamic nucleus were damaged showed a more marked and graded punishment effect of intracranial stimulation and a more profound disruption of the quantitative shock intensity-response relationship than those in which only the rostromedial part of the nucleus was damaged. Three other animals had electrodes implanted in the rostromedial hypothalamus or the midline thalamus. They showed neither the punishing effect of intracranial stimulation nor the dusruptive effect on response suppression of electrocoagulative lesions.

Animals↗
PubMedDate not supplied

Antibody-combining sites. Extending the natural limits.

The antibody repertoire is very large with at least 10(9) different antibody specificities, yet there are currently only 800 variable-region sequences known and < 23 Fab structures deposited with the Brookhaven Protein Data Bank. To engineer the antibody-combining site rationally, we need to define the rules that govern antibody structure. To understand the process of antibody-antigen recognition, we need not only to predict complementary determining regions accurately, but to simulate accurately the interaction of antibody with antigen. We have made progress in the modeling of antibody-combining sites and in the simulation of antibody complex formation. The combination of these approaches will allow us to extend the natural limits of antibody-combining sites in a more rational manner.

Algorithms↗