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Biomedical subjects

J C Craig

Publications and source records attributed to J C Craig.

At least 163 records · Page 9Linked to original sources
PubMed1980

An improved selected ion recording system for precise isotope ratio determination.

An improved analog four-channel selected ion recording system is described, in which major modifications permit a decrease in the dwell time to 33 ms per channel, thus minimizing the mass cycling error. Synchronization with a sinusoidal sweep voltage superimposed on the normal accelerating voltage (8 kV) enables two channels to be monitored simultaneously in real time and each mass to be recorded continuously. These improvements allow measurement of ion current ratios with a precision of 0.2% over a wide dynamic range, permitting accurate determination of isotopic enrichment in biomedical assays even when this enrichment is derived from a single label. Use of the system is illustrated by the analysis of palmitate turnover in dogs (using [1--13C] palmitic acid) with an average standard deviation corresponding to the detection of 0.04% excess of [1--13C] palmitate.

Animals↗
PubMed1980

Modes of vibrotactile pattern generation.

Two modes of generating vibrotactile patterns, static and scanned, were examined. In the static mode, all elements making up the pattern were turned on and off simultaneously. In the scanned mode, the pattern to be identified was moved across the tactile array. The patterns were letters of the alphabet presented to the fingertips by means of the Optacon, a reading aid for the blind. The results of the first experiment showed that the performance on a letter recognition task decreased as pattern duration decreased and that at all durations below 200-msec performance in the static mode was better than in the scanned mode. Good letter recognition was possible at durations of 4 msec in the static mode. The results of the second experiment showed that letter recognition in the static mode was highly dependent on the perceived intensity of the letters presented, whereas intensity changes in the scanned mode had little effect on letter recognition. The results of the third experiment showed that both modes of pattern presentation produced similar results in the presence of masking stimuli. The implications of the results for cutaneous pattern perception and information transmission and visual letter recognition are discussed.

Discrimination Learning↗
PubMed1979

Mechanism of the dealkylation of tertiary amines by hepatic oxygenases. Stable isotope studies with 1-benzyl-4-cyano-4-phenylpiperidine.

The microsomal oxidative dealkylation of 1-benzyl-4-cyano-4-phenylpiperidine has been studied and the source of oxygen shown to be molecular oxygen. The rate of debenzylation was decreased by substituting deuterium for hydrogen in the methylene portion of the benzyl group. The isotope effect was measured by comparison of the reaction rates of the d0 and d2 compounds 1a and 1b and also of the d5 and d7 compounds 1c and 1d. Determination of the reaction rates for various mixtures of labeled and unlabeled species allowed the rates for 0 (kH) and 100 mol % (kD) to be accurately obtained. A primary isotope effect of 1.46 was observed when the methylene hydrogens of benzyl were replaced by deuterium. No secondary isotope was observed when the aromatic hydrogens of benzyl were replaced by deuterium. The results of this study are consistent with a mechanism involving direct hydroxylation at the benzyl methylene position in a rate-determining step.

Amino Acid Oxidoreductases↗
PubMed1978

Nicotine in breast fluid of nonlactating women.

Using a combination of gas chromatography, mass spectrometry, and selected ion recording techniques, we have identified nicotine and its major metabolite, continine, in the breast fluid of nonlactating women smokers. As little as 25 picograms could be measured by using the deuterated variants, [5',5'-2H]nicotine and [3,3-2H]cotinine, both as internal standards and as carriers in an inverse isotope dilution method.

Body Fluids↗
PubMed1978

New GLC analysis of urushiol congeners in different plant parts of poison ivy, Toxicodendron radicans.

Methods are presented for the direct GLC analysis of the catechol C15 alkenyl side-chain congeners contained in the urushiol fraction of poison ivy (Toxicodendron radicans) and the C17 homologs of poison oak (Toxicodendron diversilobum). A number of liquid phases were investigated and demonstrated varying degrees of separation. The methods developed were applied to the analysis of the urushiol fractions obtained from different plant parts of poison ivy. The effects of extraction before and after drying demonstrated tht a larger percentage of urushiol was obtained when the fresh plant material was extracted with ethanol.

Catechols↗
PubMed1977

Vibrotactile pattern perception: extraordinary observers.

Two sighted peopled showed a remarkable ability to perceive vibrotactile patterns generated by the Optacon, a reading aid for the blind. These individuals were able to read at very high rates, 70 to 100 words per minute, through their fingertips. Additional testing showed them to be much better than other people at discriminating and recognizing vibrotactile patterns.

Adult↗
PubMed1977

Specific lysine labeling by 18OH- during alkaline cleavage of the alpha-1-antitrypsin-trypsin complex.

alpha-1-Antitrypsin is a serum protein that inhibits many proteolytic enzymes. Recently, it was suggested that the alpha-1-antitrypsin-trypsin complex is an acyl ester analogous to the acyl intermediate that forms between trypsin and its substrates. In previous work we showed that the alpha-1-antitrypsin-trypsin complex can be split at high pH, releasing a component of alpha-1-antitrypsin. This component had a new carboxyl-terminal lysine, and it had lost a peptide of about 4000 daltons. In order to determine whether the alpha-1-antitrypsin is bound to trypsin through the new carboxy-terminal lysine, as would be expected if the above hypothesis is correct, we split the complex in the presence of 18OH-. When the new carboxy-terminal lysine was cleaved with carboxypeptidase B, singly labeled, doubly labeled, and unlabeled lysine were recovered. These data support the hypothesis that the alpha-1-antitrypsin-trypsin complex is an acyl ester or a tetrahedral precursor that is transformed into the acyl ester form at high pH. If other enzymes are bound by a similar mechanism, the methods used may be useful in determining which amino acids on alpha-1-antitrypsin bind covalently to each enzyme.

Alkalies↗
PubMed1976

Attenuation of vibrotactile spatial summation.

Masked and quiet thresholds at several frequencies of vibratory stimuli were measured as a function of contactor area. The test site was the left index finger; the masking site was the left little finger. The quiet threshold data were consistent with previous investigations: Low-frequency stimuli showed no spatial summation, whereas high-frequency stimuli did. In the presence of a masker, spatial summation was reduced or eliminated for high-frequency stimuli, i.e., the masked threshold was, under some conditions, independent of contactor area. Low-frequency stimuli continued to show no spatial summation in the presence of a masker. The attenuation of spatial summation appears to be a direct function of the intensity of the masking stimulus. Additional measurements with the left thenar eminence as the test site showed that spatial summation could be attenuated by a masker placed on a contralateral body site. The implications of the results for quantifying the effectiveness of a masking stimulus, for the duplex mechanoreceptor hypothesis, and for the nature of spatial summation on the skin are discussed.

Adult↗