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Biomedical subjects

K A Powell

Publications and source records attributed to K A Powell.

6 recordsLinked to original sources
PubMed1988

Structural studies of nerve terminals containing melanin-concentrating hormone in the eel, Anguilla anguilla.

Eels were adapted to black- or white-coloured backgrounds and the pituitary glands were prepared for light and electron microscopy. Immunocytochemical staining was used to study the distribution of the neurohypophysial melanin-concentrating hormone in the neurointermediate lobe. The hormone was located in small, elliptical, electron-opaque neurosecretory granules, measuring approximately 120 x 90 nm. The neurones terminated on blood vessels in the centre of the neurohypophysis and on the basement membrane separating neural and intermediate lobe tissues. The results of both light and electron immunocytochemistry and of radioimmunoassay are consistent with a higher rate of hormone release from eels adapted to white backgrounds than from those adapted to black backgrounds. In addition to this, when fish that had been adapted to white tanks were transferred to black tanks, there was an accumulation of irMCH in the gland and an increased numerical density of secretory granules at nerve terminals. These results reinforce the proposal that MCH is released during adaptation to a white background, to cause melanin concentration and to inhibit MSH release, and that its release is halted in black-adapted fish.

Adaptation, Biological↗
PubMed1987

Ultrastructural demonstration that melanin-concentrating hormone-like and alpha-melanocyte-stimulating hormone-like immunoreactive molecules coexist in the same neurosecretory granules.

Using immunocytochemical methods at the electron microscope level, immunoreactivity for both melanin-concentrating hormone (MCH) and alpha-melanocyte-stimulating hormone (alpha-MSH) has been demonstrated in the carp neurohypophysis. A double-labelling technique, using colloidal gold probes of different sizes showed that immunoreactivity to both molecules coexists within the same neurosecretory granules in some neurones, while in other neurones the granules exhibit only MCH-like immunoreactivity. These observations suggest that the two immunoreactivities are attributable to separate molecules; if they are derived from the same precursor molecule, then this must be cleaved differently in the two sets of neurones. The absence of adrenocorticotropic hormone (ACTH)-like immunostaining in any neurosecretory granule might suggest the alpha-MSH-like molecule is not derived from the conventional pro-opiomelanocortin precursor.

Animals↗
PubMed1984

Single-cell protein.

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Carbohydrate Metabolism↗
PubMed1977

Ribosomal abnormality in recA mutants of Escherichia coli.

The tif-1 mutation has been shown to affect protein synthesis in vitro by increasing translational ambiguity (Ephrati-Elizur, Luther-Davies and Hayes, 1976). It is demonstrated here that some recA mutations confer similar abnormality. By comparing suitable combinations of ribosomes and soluble proteins from recA+ and recA cells the defect is shown to be associated with ribosomes. The recA mutation, which suppresses most phenotype characteristics of the tif-1 mutation (Castellazzi, George and Buttin, 1972(b)) does not suppress the ribosomal abnormality. Since the closely linked tif-1 and recA mutations lead to the expression of a common property they may be in the same gene.

Bacterial Proteins↗
PubMed1975

recA+-dependent inactivation of the lambda repressor in Escherichia coli lysogens by gamma-radiation and by tif expression.

When gamma lysogens of E. coli are induced by gamma-radiation the gamma repressor, as measured by its specific binding to gamma DNA, is rapidly inactivated by a recA+-dependent process which does not require new protein synthesis. This rapid inactivation is similar to inactivation of repressor by expression of the temperature sensitive E. coli mutation tif. In contrast, induction by UV irradiation or mitomycin C treatment requires new protein synthesis and there is a lag before the repressor is inactivated (Tomizawa and Ogawa, 1967; Shinagawa and Itoh, 1973).

Coliphages↗