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Biomedical subjects

A Stevens

Publications and source records attributed to A Stevens.

At least 271 records · Page 15Linked to original sources
PubMed1980

HLA-A, B and C antigens in South Indian families with leprosy.

Seventy-two families, selected for having at least two children affected with leprosy, were HLA typed for 57 A, B and C locus antigens recognized by the WHO Nomenclature Committee. In addition, 20 possible new "splits" were investigated. The distribution of A, B and C locus antigens in affected and unaffected family members was similar, irrespective of the type of leprosy in the family. Gene frequencies (derived by direct gene counting from 253 haplotypes), haplotype frequencies and delta values were calculated. There is evidence for heterogeneity of B5, B15, B17, Bw16 and Bw35 and for the existence of at least one A locus and one B locus antigen not previously detected. The value of the HLA system for detecting expaternal children in a highly inbred population and the effect of inbreeding on the HLA system is discussed.

Chromosome Mapping↗
PubMed1979

Simultaneous measurement of regional blood flow and glucose extraction in rat brain.

A method has been described which allows the measurement of cerebral blood flow (CBF) and solute transport across cerebral capillary wall in the same regional sample of rat brain. An inert diffusible indicator (iodoantipyrine) was used to measure a blood flow, in mixed gray and white matter, or approx. 1.0 ml/min/g. Using 3H2O as a reference molecule, the flux of [14C]D-glucose into brain was determined at blood glucose concentration levels between 0.1 and 60 mM. In all discrete areas of brain sampled, a consistent Vmax of 1.92 micromol/min/g and a Km of 8.35 mM was found. Glucose extraction by brain was inversely related to CBF, while a direct relationship was noted for glucose clearance.

Animals↗
PubMed1978

Fidelity of histone synthesis in cultured human fibroblasts.

The results in the literature to support Orgel's general error hypothesis of ageing only provide indirect evidence that errors in protein synthesis increase during senescence. This study attempts to provide direct evidence of errors in protein synthesis by measuring the misincorporation of 35S-methionine into histone H1 obtained from young and old fibroblasts (MRC-5). The conclusions that can be drawn from this study are: (a) the error level for the misincorporation of methionine into histone H1 is less than 7 methionines/10(5) amino acids and 2-3 methionines/10(4) amino acids in young and old cells respectively; (b) a methionine containing fraction associated with H1 is obtained after the final purification. The amount of this fraction increases with the age of the cell culture as does the number of methionine residues; (c) there is a variation in the complexity of H1 polypeptide chains, the complexity increasing with the age of cultured cells.

Cell Survival↗
PubMed1977

Cyclic AMP regulation of active chloride transport in the rectal gland of marine elasmobranchs.

Active transport of chloride in the salt secreting rectal gland of the dogfish Squalus acanthias is markedly stimulated by the addition of theophylline (0.01 to 5 mM) or dibutyryl cyclic AMP (0.05 mM) during in vitro perfusion. The effect occurs promptly and may persist for two hours. Specific hormonal effectors have not yet been identified. The isolated perfused rectal gland thus offers a unique opportunity to examine the cellular mechanisms of active chloride secretion.

Animals↗
PubMed1977

The inbreeding coefficients of the Hadza.

A systematic tabulation is provided of the frequency of different types of inbreeding in the Hadza. Genealogical information was obtained for 931 individuals, alive and dead. Inbreeding was encountered with 165 individuals. There were 49 different types of inbred genealogy. No attempt was made to calculate an average inbreeding coefficient and the reasons for this are given in the text.

Consanguinity↗
PubMed1977

Effect of salt on the transcription of T7 DNA by RNA polymerase from T4 phage-infected E.coli.

Transcription of T7 DNA by T4 core enzyme with host sigma is more sensitive to KCI than that by host core enzyme with host sigma. When salt is added after initiation of RNA chains has occurred, it is not inhibitory. Salt affects the binding of T4 enzyme to T7 DNA to the same degree as the binding of host enzyme. Active preinitiation complex formation is inhibited more by salt with the T4 enzyme and the inhibition is temperature-dependent.

Coliphages↗
PubMed1976

[Cervical nystagmus and functional disorders of the cervical column].

Our experience concerning the necktorsion-nystagmus has convinced us that this type of nystagmus must be elicited via a proprioceptive mechanism. The course of the curve is very suggestive, as we can state that this nystagmus changes its direction every 3-4 seconds, following exactly the stimulating movement of the chair. Our investigations resulted in another very interesting statement. Examining also a group of normal subjects, we could state that more than 50% of them presented a necktorsion-nystagmus. In a group of patients with vertigo, we could elicit in nearly the same percentage a cervical nystagmus. A significant difference between the nystagmus observed in the normals and in the pathological cases, could not be deduced from our data, except that the pathological cases showed a little more intensive necktorsion-nystagmus. A functional examination of the mobility of the cervical spine showed a significant relationship between a movement restriction of CO-C1 and the presence of necktorsion-nystagmus. This proves also the nystagmus starts via a proprioceptive mechanism, interfering with the labyrinthine in-put at the vestibular nuclei. Without doubt, the necktorsion-nystagmus is not a direct expression of a vertebro-basilar insufficiency and is even not a true pathological sign. Its clinical value is to be re-evaluated.

Humans↗
PubMed1975

Characterization of an inhibitor causing potassium chloride sensitivity of an RNA polymerase from T4 phage-infected Escherichia coli.

The nature of the inhibition by salt (KCl) of DNA-dependent RNA polymerase from T4 phage-infected Escherichia coli (T4 enzyme) was studied using holoenzyme preparations, core enzyme and sigma fractions obtained by phosphocellulose column chromatography, and sigma fractions further purified by gradient centrifugation in the presence and absence of 6 M urea. We showed with holoenzyme preparations that salt inhibits the formation of rifampicin-resistant preinitiation complexes. The inhibition was considerably reduced when a nonionic detergent (particularly of the Triton series) was included in the reaction mixtures. With T4 core enzyme and T4 sigma fractions together with the same fractions from uninfected cells (host enzyme fractions) and different DNA templates, we showed that the T4 sigma fraction plays a role in the salt-sensitive activity with T4 DNA. The salt sensitivity of the T4 sigma fraction was antagonized by Triton; it was not a function of sigma fractions isolated from phage cultures infected in the presence of chloramphenicol. As reported previously (Stevens, A. (1973), Biochem. Biophys. Res. Commun. 54, 488), the T4 sigma fraction inhibited the activity of host sigma when they were present together in reaction mixtures, particularly in the presence of salt. T4 sigma further purified by centrifugation in glycerol gradients had the same properties as the cruder fraction, and the T4-specific polypeptide of mol wt 10000 (Stevens, A. (1972), Proc. Natl. Acad. Sci. U.S.A. 69, 603) was found in the same fractions. If the glycerol gradients contained 6 M urea, the mol wt 10000 polypeptide was separated from the salt-stimulated sigma. Fractions containing the small polypeptide could be added back to produce the salt-inhibitory effects. The inhibitory activity of both the crude sigma fraction and the fractions containing the small polypeptide was inactivated at 65 degrees C. The results suggest that the mol wt 10000 protein is a salt-promoted inhibitor, but the small amounts of it which are present in purified fractions of the T4 enzyme have not yet allowed its isolation in large enough quantities to permit a detailed study of its properties.

Coliphages↗