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Biomedical subjects

R H Davis

Publications and source records attributed to R H Davis.

At least 127 records · Page 7Linked to original sources
PubMed1985

Opportunistic surveillance of child development in primary care: is it feasible?

The authors postulate that effective developmental surveillance of children, both in terms of detection of abnormalities and in maternal counselling, can be carried out by taking advantage of opportunities during ordinary consultation to identify problems and to offer advice. The results presented in this paper are part of a more detailed study in progress to compare such an opportunistic method of health surveillance with the traditional method of regular age-linked examinations provided by clinical medical officers. From a retrospective analysis of the medical records of 58 children who had reached their first birthday and who had been registered with the study practice since their birth, the authors suggest that, based upon attendance rates, opportunistic assessment of development by a general practitioner or a health visitor is more likely to encompass those children most at risk than assessment at clinics.

Child Development↗
PubMed1984

Urethral syndrome: a self limiting illness.

Thirty nine adult women who were not pregnant and had the urethral syndrome in a general practice underwent detailed microbiological investigations. Patients monitored their own symptoms, and those with persisting symptoms were entered into a randomised controlled trial of treatment with doxycycline and placebo. Chlamydia trachomatis and Neisseria gonorrhoeae were not isolated and fastidious organisms were not causally associated with the urethral syndrome. Treatment with doxycycline showed no benefit; each episode of the urethral syndrome was short and self limiting and there were no recurrences in a median observation period of 12 months.

Adolescent↗
PubMed1984

Polyphosphate-cation interaction in the amino acid-containing vacuole of Neurospora crassa.

The vacuoles of Neurospora crassa, grown in minimal medium, contain a 1:1 ratio of basic amino acids and phosphate, the latter in the form of long-chain, inorganic polyphosphate-P. Vacuoles isolated from cells depleted of polyphosphate retain basic amino acids despite the absence of over 90% of their polyphosphate. Thus, vacuolar retention of basic amino acids is not dependent upon binding to or charge neutralization by polyphosphate. Polyphosphate was found to be the only macromolecular polyanion in vacuoles of normal or phosphate-depleted cells. Gel filtration experiments revealed that about half the polyphosphate of normal vacuoles is bound strongly by vacuolar spermidine, Mg2+, and Ca2+. The polyphosphate thus occupied was not available for basic amino acid binding. We have identified about 90% of the cations of isolated vacuoles; in addition to spermidine, Mg2+, and Ca2+, the cation pool consists mainly of arginine, ornithine, histidine, lysine, and Na+, with a small amount of K+. Isolated vacuoles appear to be almost wholly impermeable to all these ions, and in vivo, vacuoles appear to be highly selective in ion uptake by an active process. The interaction of basic amino acid with the available polyphosphate was found to reduce the chemical activity of the former. In keeping with this effect, cells with abnormally high basic amino acid-polyphosphate ratios displayed greatly swollen vacuoles, indicating considerable osmotic activity of the basic amino acids and their counterions under these conditions.

Amino Acids↗
PubMed1983

Compartmentation of spermidine in Neurospora crassa.

The polyamines putrescine, spermidine, and spermine are multivalent cations that bind to anionic cell constituents such as nucleic acids. Their distribution between free and bound states within the cell is not known. Such knowledge would be important in relation to the negative control of polyamine synthesis. We report a tracer experiment in which [14C]ornithine was added to logarithmically growing Neurospora crassa mycelia. The amount and the specific radioactivity of the three polyamines thereafter suggested that new molecules of spermidine were made preferentially from new molecules of putrescine, and that new molecules of spermine were made from new molecules of spermidine. The extent of mixing of new [14C]- and resident [12C]spermidine indicated that 70% or more of the resident spermidine was sequestered, and not immediately accessible to spermine synthase. Cell fractionation revealed that about 28% of the cellular spermidine was vacuolar, and nonexchangeable with [14C] spermidine added at the time of cell breakage. We suggest that the remainder of sequestered spermidine is bound strongly to anionic sites in the cell, and is relatively inactive in the control and synthesis of polyamines.

Carbon Radioisotopes↗
PubMed1983

Methods for mycelial breakage and isolation of mitochondria and vacuoles of Neurospora.

A new and inexpensive glass-bead blender allows rapid, easy, and controlled cell breakage of Neurospora, with good organellar survival. The yield of mitochondria and vacuoles is comparable to or better than methods involving sand grinding or snail-gut digestion of cell walls. A method for removing cell wall fragments from a crude homogenate is described. Isolation of mitochondria and vacuoles from the crude homogenate with little cross-contamination is accomplished by density-gradient centrifugation in a fixed-angle rotor (Sorvall).

Cell Fractionation↗
PubMed1983

Control of the ornithine cycle in Neurospora crassa by the mitochondrial membrane.

In Neurospora crassa, the mitochondrial membrane separates ornithine used in arginine biosynthesis from ornithine used in the arginine degradative pathway in the cytosol. Ornithine easily exchanges across the mitochondrial membrane under conditions appropriate for synthesis of the immediate biosynthetic product, citrulline. Neither of the two mitochondrial enzymes required for the ornithine-to-citrulline conversion is feedback inhibitable in vitro. Nevertheless, when arginine is added to cells and cytosolic ornithine increases as arginine degradation begins, the rate of citrulline synthesis drops immediately to about 20% of normal (B. J. Bowman and R. H. Davis, Bacteriol. 130:285-291, 1977). We have studied this phenomenon in citrulline-accumulating strains carrying the arg-1 mutation. Citrulline accumulation is blocked when arginine is added to an arg-1 strain but not to an arg-1 strain carrying a mutation conferring insensitivity of intramitochondrial ornithine synthesis to arginine. Thus, ornithine is evidently unable to enter mitochondria in normal (feedback-sensitive) cells. Other experiments show that cytosolic ornithine enters mitochondria readily except when arginine or other basic amino acids are present at high levels in the cells. We conclude that in N. crassa, the mitochondrial membrane has evolved as a secondary site of feedback inhibition in arginine synthesis and that this prevents a wasteful cycling of catabolic ornithine back through the anabolic pathway. This is compared to the quite different mechanism by which the yeast Saccharomyces cerevisiae prevents a futile ornithine cycle.

Arginine↗
PubMed1982

Polyamine-deficient Neurospora crassa mutants and synthesis of cadaverine.

The polyamine path of Neurospora crassa originates with the decarboxylation of ornithine to form putrescine (1,4-diaminobutane). Putrescine acquires one or two aminopropyl groups to form spermidine or spermine, respectively. We isolated an ornithine decarboxylase-deficient mutant and showed the mutation to be allelic with two previously isolated polyamine-requiring mutants. We here name the locus spe-1. The three spe-1 mutants form little or no polyamines and grow well on medium supplemented with putrescine, spermidine, or spermine. Cadaverine (1,5-diaminopentane), a putrescine analog, supports very slow growth of spe-1 mutants. An arginase-deficient mutant (aga) can be deprived of ornithine by growth in the presence of arginine, because arginine feedback inhibits ornithine synthesis. Like spe-1 cultures, the ornithine-deprived aga culture failed to make the normal polyamines. However, unlike spe-1 cultures, it had highly derepressed ornithine decarboxylase activity and contained cadaverine and aminopropylcadaverine (a spermidine analog), especially when lysine was added to cells. Moreover, the ornithine-deprived aga culture was capable of indefinite growth. It is likely that the continued growth is due to the presence of cadaverine and its derivatives and that ornithine decarboxylase is responsible for cadaverine synthesis from lysine. In keeping with this, an inefficient lysine decarboxylase activity (Km greater than 20 mM) was detectable in N. crassa. It varied in constant ratio with ornithine decarboxylase activity and was wholly absent in the spe-1 mutants.

Cadaverine↗