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Biomedical subjects

G R Smith

Publications and source records attributed to G R Smith.

At least 289 records · Page 16Linked to original sources
PubMed1980

Infrared laser photolysis: a new tool for the study of prebiotic chemistry.

Infrared laser induced dielectric breakdown and multiphoton absorption experiments on CH4/NH3 'atmospheres' are described. It is found that HCN, a central intermediate in prebiotic chemistry, is a principle product. This, combined with the fact that dielectric breakdown appears to have much in common with ordinary electric sparks, suggests that the laser could be a useful tool in studies of prebiotic chemistry. Several possible experiments in this vein are suggested.

Ammonia↗
PubMed1980

Unwinding and rewinding of DNA by the RecBC enzyme.

Under physiological conditions the initial action of the RecBC enzyme (exonuclease V) on duplex DNA is unwinding of the DNA strands. We have examined by electron microscopy the initial products of this unwinding reaction. When such reactions are carried out in the presence of DNA binding protein, unwinding structures are seen both at the terminus of the duplex DNA and at locations remote from the ends of the DNA molecule. Both terminal and internal unwinding structures proceed along DNA at about 300 nucleotides per second, and the single-stranded loops in both types of structure enlarge at about 100 nucleotides per second. In the internal unwindings DNA must be rewound behind the enzyme at about 200 nucleotides per second. The structures do not occur on supercoiled or nicked circular DNA, indicating that free ends are needed for their formation. In the absence of DNA binding protein only internal unwinding structures are seen, suggesting that the internal structures are formed from the terminal unwindings by base-pairing of their unwound single-strand tails. We present a model which incorporates these structures and is consistent with previous observations on the unwinding and degradative actions of the enzyme. In this model the enzyme travels through duplex DNA by unwinding the DNA ahead of itself and rewinding it behind itself. The internal unwindings produced by the RecBC enzyme could be active in initial synapsis step in genetic recombination.

DNA↗
PubMed1980

Generalized recombination: nucleotide sequence homology between Chi recombinational hotspots.

Chi sites stimulate generalized recombination catalyzed by the RecA-RecBC-dependent system of E. coli. This stimulation occurs over a region of several thousand base pairs surrounding the Chi site. These sites arise by mutation at four distinct loci in bacteriophage lambda. We report here the nucleotide sequence surrounding one of these loci, chi B, located between the xis and reda genes. Alteration of a single GC base pair, by deletion or by transversion to a CG base pair, creates the Chi recombinational hotspot chi + B. In a section of 30 bp, the chi + B sequence has 23 bp in common with the chi + C sequence determined previously. We presume that some part of this common sequence is the recognition sequence for a protein which acts at a rate-limiting step of generalized recombination.

Bacteriophage lambda↗
PubMed1980

Further studies on caprine and ovine mycoplasmas related to Mycoplasma mycoides subsp. mycoides.

Nine caprine and ovine mycoplasma strains, said to be indistinguishable serologically from Mycoplasma mycoides subsp. mycoides (the causative organism of contagious bovine pleuropneumonia; CBPP) were examined in mice by (1) a mycoplasmaemia test, and (2) a cross-protection test. Of the nine strains, two from goats belonged to a small colony (SC) type; four caprine and three ovine strains belonged to a large colony (LC) type.The two SC strains - like a single SC strain examined in an earlier study - were indistinguishable from genuine M. mycoides subsp. mycoides as isolated from CBPP. They produced mycoplasmaemia readily. In a cross-protection test, the two SC strains and a CBPP strain immunized completely against each other.Of the seven LC strains, six - like six LC strains examined in an earlier study - were easily distinguished from genuine M. mycoides subsp. mycoides; except for one that was not tested, all were shown to lack the ability to produce mycoplasmaemia readily. In cross-protection tests all six strains immunized partially but not completely against a CBPP strain.The seventh LC strain (Mankefår 2833) was exceptional: it produced mycoplasmaemia readily, resembling the SC strains in this respect. Like other LC strains, in cross-protection tests it protected only partially against a CBPP strain. Strain Mankefår 2833 was isolated in ca. 1965 by Brack from a Barbary sheep (Ammotragus lervia) in a German zoo.The ability of Mankefår 2833 to produce mycoplasmaemia enabled it to be used as a challenge strain in cross-protection tests. For the purpose of such tests the collection of nine mycoplasma strains referred to above was augmented with six LC strains from an earlier study. Partial but not complete protection against Mankefår 2833 was produced by two caprine SC strains, one CBPP strain, and nine LC strains. Three further LC strains gave protection that may have been as strong as that produced by the homologous strain, but confirmatory experiments are needed. A strain of M. mycoides subsp. capri gave no protection against Mankefår 2833.

Animals↗
PubMed1980

Clostridium botulinum in British soil.

Soil samples from various parts of Britain were examined for Clostridium botulinum by a sensitive technique comparable with that recently used for mud samples from British aquatic environments. The results showed beyond doubt that in Britain the prevalence of the organism in soil is much lower than in mud. Of 174 samples from all sites examined only 10 (5 . 7%) could be shown to contain Cl. botulinum; this finding was consistent with the results of surveys made by less sensitive techniques in 1922, 1928 and 1942. No type other than B was found. The evidence suggested that in certain localized areas the prevalence was likely to be high. Three sites associated for many years with animals were included in the survey; at the Zoological Society's premises at Regent's Park and Whipsnade, and at the Market paddocks, Gorgie, Edinburgh, the prevalence of Cl. botulinum was either very low, or nil. In an earlier survey of the redeveloped site of the former Metropolitan Cattle Market, London, 25% of soil samples gave a positive result and no less than four types (B, C, D. and E) were demonstrated.

Clostridium botulinum↗
PubMed1980

Effect of prenatal drug administration on maternal and neonatal platelet aggregation and PF4 release.

Release of platelet antiheparin activity (platelet factor 4, PF4) induced by collagen and l-epinephrine, is normal in newborn infants without antenatal drug exposure. In contrast, PF4 release in platelets of infants of mothers with membrane-stabilizing drug ingestion is decreased to a greater extent than in their respective mothers. Platelet aggregation gives a qualitative indication of response. Platelets of mothers with antenatal drug exposure and those of their infants showed only a one-wave response to adenosine diphosphate, while platelets of these same mothers still showed a two-wave aggregation response to l-epinephrine. In contrast, platelets of all neonates lacked epinephrine-induced aggregation response, even when washed and resuspended in adult plasma. Our studies show that prenatal drugs have an effect on the platelet release mechanism in both mothers and their exposed infants; but the effect on the epinephrine-induced platelet response is less in mothers. Newborn infants have different aggregation and platelet release response to epinephrine which suggests that platelet aggregation and the release reaction can occur independently of each other.

Adenosine Diphosphate↗
PubMed1980

Detailed activation sequence in the region of electrically induced ventricular fibrillation in dogs.

We determined the details of ventricular activation sequence during the onset of ventricular fibrillation in 6 dogs. Unipolar electrograms were simultaneously recorded from 192 ventricular epicardial sites evenly spaced in a 3 by 3 cm square area surrounding 2 central sites to which stimuli for inducing fibrillation were delivered. In 5 dogs, 2 to 10 msec duration pulses with amplitudes of 150 to 220 v were used to induce fibrillation, and in 1 dog, 3 successive permature stimuli of 3 v intensity were used to induce fibrillation. In 2 dogs the pattern of activation at the onset of fibrillation was compatible with local reentrant paths near the stimulus site. Fibrillation was induced with a single high intensity pulse in both of these dogs. In the other 4 dogs, the pattern of activation at the onset of fibrillation was highly suggestive of reentrant paths distant from the stimulating electrodes. In 3 of these dogs fibrillation was induced by a single high intensity pulse and in the other it was induced by 3 repetitive stimuli. Activation patterns resembling supraventricular activation occurred prior to fibrillation in the latter animal. The data demonstrate 2 distinct modes of onset of electrically induced ventricular fibrillation. The findings support local reentry in the region of the stimulus site as the mode of onset of fibrillation in some animals and possible reentry at sites distant from the stimulus site with participation of the specialized conduction system in other animals. The differences in mode of onset of electrically induced fibrillation may be responsible for instability of fibrillation threshold measurements in some animals. In addition the role of the specialized conduction system in the onset of fibrillation may be responsible for the effects of sympathetic and vagal stimulation on fibrillation threshold.

Animals↗
PubMed1979

Clostridium botulinum in soil on the site of the former Metropolitan (Caledonian) Cattle Market, London.

Sixty soil samples were collected from the redeveloped site of the former Metropolitan (Caledonian) Cattle Market, Islington, London. Of these, 15 (25%) contained Clostridium botulinum and no less than four types (B, C, D and E) were demonstrated. Early British soil surveys suggested that only 4--8% of samples contained Cl. botulinum (type A or B). Although there can be no absolute proof, it seems likely that the striking prevalence at the Market site was the result of faecal contamination by a small proportion of the many millions of farm animals brought there from elsewhere. The distribution of Clostridium tetani was uneven, but of 18 soil samples taken from one area of the Market site, 16 (89%) were positive.

Animals↗
PubMed1979

Differentiation of Mycoplasma mycoides subsp. mycoides from certain closely related caprine mycoplasmas by mycoplasmaemia and cross-protection tests in mice.

In recent years, mycoplasma taxonomists have found that numerous mycoplasma strains from goats are serologically indistinguishable from Mycoplasma mycoides subsp. mycoides, the causative agent of contagious bovine pleuropneumonia (CBPP), by routinely used tests, e.g. the metabolism- and growth-inhibition tests. As a result, such organisms are now openly referred to as M. mycoides subsp. mycoides. Seven of these so-called M. mycoides subsp. mycoides strains from goats were compared with two strains of M. mycoides subsp. mycoides from CBPP, and with one strain of M. mycoides subsp. capri, by means of two in-vivo tests, namely, (1) a test of the ability of each strain, injected intraperitoneally into mice, to produce mycoplasmaemia, and (2) a cross-protection test in mice. Of the seven strains, only one ('O goat') was indistinguishable from genuine M. mycoides subsp. mycoides; it also had small colonies resembling those of genuine M. mycoides subsp. mycoides. The other six were easily distinguished from genuine M. mycoides subsp. mycoides, and they produced large colonies. These six strains and others like them should no longer be given a name that fails to distinguish them from the causative agent of CBPP. Cross-protection tests showed that the seven goat strains referred to above differed from M. mycoides subsp. capri.

Animals↗
PubMed1979

Evolution of polypyrimidines in Drosophila.

We surveyed 101 different Drosophila species for the presence of a particular highly repetitive DNA sequence containing long tracts of polypyrimidine/polypurine DNA, first found in D. melanogaster. Out of 55 tested species in the melanogaster group, only the sibling species D. simulans and D. mauritiana, as well as one distant relative in the ananassae subgroup, D. varians, contained the same sequence. All four of these species have long pyrimidine tracts as shown by acid hydrolysis of labelled DNA. All four species have the same sequence, bu the amount of this polypyrimidine/polypurine DNA varies greatly. Four other species in the hydei subgroup were found to contain a polypyrimidine/polpurine sequence, with an oligonucleotide composition different from that of D. melanogaster. This polypyrimidine DNA varies from as much as 10% of the total DNA in D. nigrohydei, to as little as 0.4% in D. neohydei. The long pyrimidine tracts in the hydei subgroup are often more than a thousand nucleotides in length, representing exceedingly homogeneous repetitious sequences.--These results show a rapid but discontinuous pattern of evolution for polypyrimidine/polypurine DNA . These sequences are not species specific, yet closely related species have greatly different amounts of polypyrimidines. Drastic changes occur in the amounts of these satellite type DNA sequences, as if the sequence had no continuous selective advantage in evolution. The implications of these results with regard to the general function and evolution of satellite DNA are discussed.

Animals↗
PubMed1978

Clostridium botulinum in aquatic environments in Great Britain and Ireland.

Mud samples from aquatic environments in many parts of Great Britain and Ireland were collected, mainly in 1975 and 1976, and examined for Clostridium botulinum. The samples were taken from lakes, ponds, reservoirs, marshes, mudflats, streams, rivers and canals, and the sampling areas included a number of bird refuges and reserves. Of 554 samples 194 (35.0%) were positive and 167 (30.1%), 19 (3.4%), 6 (1.1%) and 15 (2.7%) contained types B, C, D and E respectively; 13 (2.3%) contained more than one type. Each type demonstrated was found in both fresh-and salt-water environments. Type B was widespread; types C, D and E were demonstrated in widely separated areas in England and Wales, and type C was found in both the north and south of Scotland. The results were compared with those reported earlier in respect of surveys in the London area, the Norfolk Boads and the Camargue (France).

Clostridium botulinum↗
PubMed1978

A single base-pair change creates a Chi recombinational hotspot in bacteriophage lambda.

X4+ mutations, responsible for the Chi phenotype in phage lambda, locally increase the rate of recombination promoted by the Escherichia coli recombination system (Rec). X+ mutations in the cII gene, one of a few sites in lambda at which such mutations arise, were located genetically and physically with overlapping deletions. DNA sequence analysis of the deletion segment containing the X+ C mutations showed that two independent X+ C mutations arose by the same A-T to T-A transversion. Presumably, this change creates a nucleotide sequence recognized by a protein involved in a rate-limiting step of recombination.

Base Sequence↗