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Biomedical subjects

R M Brown

Publications and source records attributed to R M Brown.

At least 163 records · Page 9Linked to original sources
PubMed1976

Cellulose microfibrils: visualization of biosynthetic and orienting complexes in association with the plasma membrane.

Cellulose microfibril biosynthesis, assembly, and orientation in the unicellular green alga, Oocystis, is visualized in association with a linear enzyme complex embedded in the B face of the plasma membrane. Granule bands of the A face and complementary ridges of the B face are postulated to assist in the orientation of recently synthesized microfibrils. A model for microfibril synthesis and orientation is proposed and correlated with current hypotheses regarding cellulose biosynthesis in higher plants.

Cell Membrane↗
PubMed1976

Cellulose biosynthesis in Acetobacter xylinum: visualization of the site of synthesis and direct measurement of the in vivo process.

In vivo synthesis of cellulose by Acetobacter xylinum was monitored by darkfield light microscopy. Cellulose is synthesized in the form of a ribbon projecting from the pole of the bacterial rod. The ribbon elongates at a rate of 2 mum min-1. The ribbon consists of approximately 46 microfibrils which average 1.6 X 5.8 nm in cross section. The observed microfibrillar elongation rate corresponds to 470 amol of glucose/cell per hr assimilated into cellulose. Electron microscopy of the process using negative staining, sectioning, and freeze-etching indicated the presence of approximately 50 individual synthetic sites organized in a row along the longitudinal axis of the bacterial rod and in close association with the outer envelope. The process of cellulose synthesis in Acetobacter is compared with that in eukaryotic plant cells.

Cellulose↗
PubMed1976

Zinc nutrition of preschool children in the Denver Head Start program.

Low income diets provide relatively little zinc. This study was designed to evaluate the zinc nutritional states of 74 low income preschool children enrolled in the Denver Head Start Program. Zinc is necessary for normal growth, hence children were selected on the bases of low height percentiles. The mean (+/- SE) hair zinc concentration was 87.0 +/- 5.9 mug/g, and the mean plasma zinc concentration was 74.5 +/- 1.5 mug/100 ml. These levels were both lower (P is less than 0.005) than those of middle income children of similar age. Sixty-eight percent of the study group had a hair zinc concentration less than 70 mug/g and/or a plasma zinc concentration less than 68 mug/100 ml. These results indicate that inadequate zinc nutrition may be common among preschool children with low growth percentiles from low income families.

Body Height↗
PubMed1976

Electron microscopy of the cotton fibre: new observations on cell wall formation.

The ultrastructure of the cotton fibres was examined after developing successful fixation methods. Fibre cells were fixed at different stages of development. In cells which were elongating and producing primary cell walls, the Golgi apparatus appeared to be directly involved in secretion and synthesis of primary wall components. In cells which were synthesizing thick secondary cell walls, evidence suggested a major role for the endoplasmic reticulum and plasma memebrane in the synthesis and secretion of secondary wall materials. The possibility of a shift from a Golgi apparatus pathway for primary wall synthesis to an endoplasmic reticulum pathway for secondary wall synthesis is discussed. Plasma membrane micro-invaginations are present only during secondary wall synthesis and may represent sites of cellulose assembly. A model for primary wall biogenesis via the Golgi apparatus is presented, and the potential of the cotton fibre as a model system for studying cellulose biogenesis in higher plants is discussed.

Cell Membrane↗
PubMed1975

Functional and biochemical aspects of catecholamine metabolism in brain under hypoxia.

Animals exposed to 6% oxygen showed a partial inhibition of the rate of tyrosine hydroxylation and a blockade of the conditioned avoidance response. The behavioral disruption was suggested to result, at least in part, from a dopaminergic disturbance, since the behavior was restored by the administration of DOPA or apomorphine but not by 5-hydroxytryptophan. Biochemical data showed a selective retardation in brain dopamine (DA) disappearance after synthesis inhibition. Methoxytyramine formation was markedly retarded. Analysis of this effect indicated that the decreased DA turnover was related to the release of transmitter rather than to an effect on catechol-O-methyltransferase (COMT) or monoamine oxidase (MAO). In addition, there was evidence for a partial inhibition of MAO activity by hypoxia as well as a decreased activity of dopamine-betahydroxylase. It was concluded that the disruption of behavior was related to decreased dopaminergic receptor activation and that decreased synthesis played at most a contributory role.

5-Hydroxytryptophan↗
PubMed1975

Acute and subacute inhalation toxicities of phosphine, phenylphosphine and triphenylphosphine.

The four-hour LC50 values for ChR-CD male rats for phosphine, phenylphosphine and triphenylphosphine have been determined to be 0.44 micromoles per liter (muM/liter), 1.56 muM/liter and 47.8 muM/liter respectively. The dose-death curves are parallel. During exposure, all three caused clinical signs indicative of mild respiratory irritation. Triphenylphosphine also caused severe weight loss immediately after exposure, followed by normal rate of weight gain. No histopathologic effects due to exposure were seen in any of the tissues examined after single exposures to any of the three compounds. Phosphine and triphenylphosphine caused mild weight loss during a 10-day exposure period followed by normal rate of weight gain during a 14-day recovery period. The phenylphosphine exposures caused a decreased rate of weight gain during the exposure period which returned to normal during the recovery period. Silver nitrate paper was found to be unsuitable for field analysis of phenylphosphine.

Air Pollutants↗
PubMed1974

The relationship of gamone to the mating reaction in Chlamydomonas moewusii.

Gamete-gamete adhesion in Chlamydomonas has long been attributed to large glycoprotein particles (gamone) on the flagellar membrane surface. These macromolecules may be incidentally sloughed off or released into the medium. Gamone isolated from the medium of one mating type will cause isoagglutination of opposite gametes. Our study of Chlamydomonas moewusii shows that such particles isolated from the cell medium are really membrane vesicles with mastigonemes (flagellar appendages) attached. The vesicles appear to bleb off the flagellar membrane as a normal process. Purified mastigonemes have no isoagglutinating activity, while purified membrane vesicles (with no mastigonemes attached) retain activity. Therefore, the large particles isolated by others from the cell medium of Chlamydomonas and thought to be equivalent to the gametic adhesion substance are in fact membrane vesicles upon which the adhesion sites are located, and these sites are probably much smaller than was previously supposed. Mastigonemes appear to have no role in gamete adhesion.

Agglutination↗