PubMed Health⌕ Search

Biomedical subjects

J C LEWIN

Publications and source records attributed to J C LEWIN.

11 recordsLinked to original sources
PubMed1965

STUDIES ON THE BIOCHEMISTRY AND FINE STRUCTURE OF SILICA SHELL FORMATION IN DIATOMS. I. THE STRUCTURE OF THE CELL WALL OF CYLINDROTHECA FUSIFORMIS REIMANN AND LEWIN.

An electron microscope study on the cell wall of the diatom Cylindrotheca fusiformis was carried out using stereoscopic and sectioning techniques. Material prepared by an enzyme treatment or by a mechanical method showed that the wall consists of two major components: a silica shell and organic material. Vapor of hydrofluoric acid was employed to remove the silica and thereby reveal the arrangement of the organic material. An attempt was made to increase the contrast of the organic component by "staining." Uranylacetate not only increased the electron opacity of the organic material but also apparently decreased the electron opacity of the silica shell. In ultrathin sections of complete cells, the structure as revealed by stereoscopy could be confirmed and extended. Every part of the silica shell is tightly enclosed by organic material. In the valve region the silica enclosed in this way is located between other layers of organic material. The whole cell wall is surrounded by a mucilaginous substance which stains with ruthenium red.

Biochemical Phenomena↗
PubMed1963

DIATOMS.

Explore the source record for details and available documents.

Anatomy↗
PubMed1955

Silicon metabolism in diatoms. III. Respiration and silicon uptake in Navicula pelliculosa.

1. Evidence is presented that silicon uptake in the diatom Navicula pelliculosa is linked with aerobic respiration. 2. Cyanide, fluoride, iodoacetate, arsenite, azide, and fluoroacetate, at concentrations inhibitory to respiration, were also inhibitory to silicon uptake. 3. 2,4-Dinitrophenol (1 to 2 x 10(-5)M) stimulated respiration by 100 per cent, but almost completely inhibited silicon uptake. 4. The respiratory quotient of non-Si-deficient cells decreased from 0.93 to 0.75 after 4 days of starvation in darkness. Glucose (1 per cent) raised the respiratory quotient of such starved cells to 1.05. 5. Silicate (20 mg. Si/liter) stimulated respiration of unstarved Si-deficient cells by about 40 per cent. The effect of silicate on the respiration of Si-deficient cells which had been starved in darkness for 4 days was less marked. 6. The respiratory quotient of Si-deficient cells decreased from 0.8-0.9 to 0.3 after 4 days of starvation in darkness. The addition of silicate to starved cells raised the quotient to 0.5. This represented a 25 per cent stimulation of oxygen uptake concomitant with a 90 per cent stimulation of carbon dioxide evolution. 7. Glucose (1 per cent) caused an increase of respiratory quotient in starved cells from 0.3 to 0.7-0.8. The addition of silicate had no effect on the R.Q. during the oxidation of exogenous glucose. 8. Substrates (glucose, fructose, galactose, lactate, succinate, citrate, glycerol), which caused a stimulation of respiration in starved cells, also stimulated silicon uptake by those cells. However, the stimulation of silicon uptake (50 to 100 per cent) was not proportional to the respiratory stimulation by these substrates (30 to 300 per cent).

Diatoms↗
PubMed1954

Silicon metabolism in diatoms. I. Evidence for the role of reduced sulfur compounds in silicon utilization.

1. Cells of the fresh water diatom Navicula pelliculosa may be grown in a mineral medium containing a low concentration of silicon. When transferred to a fresh silicate solution and incubated under non-growing conditions such deficient cells rapidly take up silicon from the medium. 2. The utilization of silicon is an aerobic process. 3. When deficient cells are washed with distilled water or saline, their ability to utilize silicon is impaired whereas respiration is unaffected. 4. The ability of washed cells to take up silicon can be partially restored with sulfate or ascorbic acid, and is completely restored by Na(2)S, Na(2)S(2)O(3), glutathione, l-cysteine, dl-methionine, or ascorbic acid plus sulfate. 5. The sulfhydryl reagent, CdCl(2), inhibits silicon utilization of unwashed cells at concentrations which do not affect respiration. This inhibition similarly is reversed by glutathione or cysteine. 6. However, sodium iodoacetate or sodium arsenite inhibits respiration and silicon utilization at the same concentrations. 7. The silicon taken up by deficient cells is deposited at the cell surface as a thickening of the existing silica frustules. 8. Sulfhydryl groups in the cell membrane may be involved in silicon uptake by diatoms.

Cell Membrane↗