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Biomedical subjects

C Kennedy

Publications and source records attributed to C Kennedy.

At least 307 records · Page 17Linked to original sources
PubMed1978

Polarity of mutations induced by insertion of transposons Tn5, Tn7 and Tn10 into the nif gene cluster of Klebsiella pneumoniae.

Three new genes nifM, nifI and nifN have been mapped in the nif gene cluster of Klebsiella pneumoniae and a fourth gene nifJ has been confirmed as being a separate cistron. Polar nif mutations were obtained by transposition of Tn7 to plasmid pRD1, and of Tn5 and Tn10 to plasmid pMF100, a derivative of pRD1. Complementation analysis of the nif::Tn mutants led to the identification of at least six transcriptional units: nifB; nifA; nifJ; nifH, nifD and nifK; nifE and nifI; nifN, nifM and nifF. Biochemical and genetic evidence suggest that the three genes nifH, nifD and nifK, which are probably the structural genes for nitrogenase, belong to the same operon and are transcribed from nifH to nifK. A polypeptide with a molecular weight of approximately 120,000 is presumed to be the nifJ product.

Chromosome Mapping↗
PubMed1978

Functional plasticity in the immature striate cortex of the monkey shown by the [14C]deoxyglucose method.

Autoradiographic representation of the local rates of cerebral glucose utilization and local cerebral functional activity by means of the [14C]deoxyglucose technique reveals the existence of the ocular dominance columns in the striate cortex of the monkey in the first day of life. In contrast to the stability of these columns in more mature brain, monocular deprivation for 3 months from the first day of life results in their complete disappearance and a reversion of the autoradiographic pattern to that seen in animals with normal binocular vision. These results are consistent with a reorganization of the representation of the visual fields of the two eyes in the striate cortex and provide additional evidence of the plasticity of the striate cortex of the monkey in early life.

Animals↗
PubMed1978

Local cerebral glucose utilization in the normal conscious macaque monkey.

The [14C]deoxyglucose method for quantitative determination of local cerebral glucose utilization was extended to the macaque monkey. The necessary constants required by its operational equation were evaluated. The lumped constant, measured in 7 normal conscious monkeys, was found to equal 0.344 (SEM, +/- 0.036). The rate constants were also estimated and found to be very similar to those obtained previously in the rat. With these essential constants evaluated, the method was applied to normal conscious monkeys. Local cerebral glucose utilization was found to vary marked throughout the brain but to fall within two distributions, a higher one in gray matter and lower one in white matter. In general, the values fell in a range to be expected from previous measurements of average energy metabolism in the brain as a whole. The values were considerably lower than those observed previously in the conscious rat. Marked heterogeneity of rates of glucose utilization were observed in a number of anatomical structures. In some cases the patterns of heterogeneity were consistent with known histological cytoarchitecture; in others the heterogeneity did not conform with known cytoarchitectural features but corresponded to patterns previously demonstrated by electrophysiological techniques. Many of the regions of the cerebral cortex showed columnar patterns of distribution of higher and lower rates of glucose utilization. These may be a metabolic reflection of the columnar organization of function within the cerebral cortex.

Animals↗
PubMed1978

Nitrogenase synthesis in Klebsiella pneumoniae: comparison of ammonium and oxygen regulation.

Rates of nitrogenase synthesis by Klebsiella pneumoniae were measured by pulse-labelling organisms with a mixture of 14C-labelled amino acids followed by sodium dodecyl sulphate gel electrophoresis and autoradiography. Populations from an NH4+-repressed, SO42--limited chemostat (0.46 mg dry wt ml-1), when released from NH4+ repression, simultaneously synthesized detectable quantities of the three nitrogenase polypeptides 45 min before acetylene-reducing activity was observed. Exposure of populations synthesizing nitrogenase to air or NH4+ (200 microgram N ml-1) repressed synthesis of both component proteins simultaneously, the rate initially decreasing by half in 11 to 12 min; in the presence of NH4+ a second slower phase with an approximate half-life of 30 min was observed. With 5% O2 in N2 the half-lives for the decreases in the rates of synthesis were 30 min for the Fe protein and 33 min for the Mo-Fe protein. Oxygen also repressed nitrogenase in a glutamine synthetase constitutive derivative of K. pneumoniae (strain SK24) which escapes NH4+ repression. Regulation of nitrogenase by O2 may therefore be independent of glutamine synthetase.

Ammonia↗
PubMed1978

Transmucosal potential difference; diagnostic value in gastro-oseophageal reflux.

Nineteen patients with symptoms of upper gastrointestinal disease were assessed by endoscopy. Transmucosal potential difference (PD) in the lower oesophagus was recorded and suction biopsy specimens were obtained from the site of measurement and examined by light microscopy after haematoxylin and eosin staining. In 10 patients with normal histology, mean PD was--14.4 mV (SEM +/- 0.4 mV), whereas in nine patients with histological changes of reflux mean was +9.4 mV (SEM +/- 3.0 mV). In this latter group, polarity of the PD was reversed in all but one case. Good correlation was found between these objective indices of lower oesophageal disease and the presence of symptoms such as dysphagia and heartburn. The visual appearance at endoscopy was less reliable. It is suggested that measurement of PD is a simple, rapid, and sensitive method of detecting the presence of oesophageal mucosal damage.

Adult↗
PubMed1978

Measurement of local cerebral blood flow with iodo [14C] antipyrine.

The autoradiographic diffusible tracer technique for the measurement of local cerebral blood flow was originally designed for use with the radioactive, inert gas 131I-labeled trifluoroiodomethane and is applicable only with tracers that exhibit unrestricted diffusion through the blood-brain barrier. Because of the technical problems associated with the use of gaseous tracers, a suitable nonvolatile tracer has been sought. [14C] Antipyrine has been used previously and found to be unsuitable because of limitations in its diffusion through the blood-brain barrier. An analogue of [14C]antipyrine, iodo [14C]antipyrine, exhibits higher partition coefficients than [14C]antipyrine between nonpolar solvents and water and might, therefore, be expected to diffuse more freely through the barrier. Its use as the tracer in the local blood flow technique leads to values considerably above those obtained with [14C]antipyrine in the rat and cat and essentially the same as those obtained with the gas trifluoro[131I]iodomethane in the cat. Iodo[14C]antipyrine appears, therefore, to be a satisfactory nonvolatile tracer for the measurement of local cerebral blood flow.

Animals↗
PubMed1977

Complementation analysis of Klebsiella pneumoniae mutants defective in nitrogen fixation.

A series of mutants defective in nitrogen fixation (nif) were isolated in Klebsiella pneumoniae strain M5a1. The nif mutations were either located on plasmid pRD1 or on the K. pneumoniae chromosome. A total of 37 plasmid mutants and 28 chromosomal mutants were employed in complementation tests using the acetylene reduction technique. Most mutants could be assigned to one of seven nif cistrons: nifA, nifB, nifD, nifE, nifF, nifH, and nifK. Complementation analysis of two nif deletion mutants confirmed transductional evidence that these strains carry nifB-A-F deletions. One deletion mutant had, in contrast to previous transductional analysis, a functional nifK cistron and presumably is deleted for nifB-A-F-E. Examination of the biochemical phenotype of several mutants suggests that the nifA product has a regulatory function, and nifK, nifD and nifH are most probably the structural genes for nitrogenase.

Chromosomes, Bacterial↗
PubMed1977

Linkage map of the nitrogen fixation (nif) genes in Klebsiella pneumoniae.

The nif cistrons indentified by complementation analysis in the preceding paper (Dixon et al., 1977) were mapped with respect to hisD and to each other other by P1 cotransduction and three-factor reciprocal crosses. The order obrained was hisD nifB nifA (nifL) nifF nifE nifK nifD nifH. Analysis of hisD2-nif cotransduction data by the Wu equation (Wu, 1966) suggested that the nif genes are divided into two clusters: a his-proximal cluster comprising nifBA(L)F and a his-distal group of nifEKDH.

Chromosome Mapping↗
PubMed1977

Expression of Klebsiella pneumoniae nitrogen fixation genes in nitrate reductase mutants of Escherichia coli.

Nitrate reductase (nar) A, B and E mutants of Escherichia coli with plasmids carrying Klebsiella pneumoniae nitrogen fixation (nif) genes reduced acetylene independently of added molybdate, but nar D mutants showed pleiotropic dependence on the concentration of added molybdate for expression of both nar and nif. No complementation of nar mutations by nif occurred; nitrite but not nitrate repressed nif in nar hosts. Derepression of nif occurred in molybdenum-deficient nar D (nif) strains since nitrogenase peptides were present. nifB mutants, thought to have a lesion in the pathway of molybdenum to nitrogenase, as well as nif deletion mutants, had normal nitrate reductase activity.

Enzyme Repression↗