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Biomedical subjects

E Gantt

Publications and source records attributed to E Gantt.

50 records · Page 3Linked to original sources
PubMed1973

Phycobilisomes from a blue-green alga Nostoc species.

Phycobilisomes were isolated from a Nostoc sp. strain Mac in phosphate buffer (pH 7.0) by treatment with 1% Brij 56 and centrifugation on discontinuous sucrose gradients (2.0, 1.0, 0.5, and 0.25 M in the proportions 6:4:4:10 ml, respectively). Absorption spectra of isolated phycobilisomes showed the presence of phycoerythrin, phycocyanin, and allophycocyanin. The phycobilisome pigments were partially resolved by electrophoresis on acrylamide gels. Stained gels demonstrated that each main protein band corresponded to a pigmented region. The phycobilisomes appeared compact with a rounded surface and flattened base (about 40-nm diameter) at the attachment site to the photosynthetic lamellae. Fixation in glutaraldehyde caused a significant reduction in total pigment absorption, as well as shifts in the absorption maxima, particularly that of phycoerythrin.

Cell Membrane↗
PubMed1972

Phycobilisomes of Porphyridium cruentum. I. Isolation.

A procedure was developed for the isolation of phycobilisomes from Porphyridium cruentum. The cell homogenate, suspended in phosphate buffer (pH 6.8), was treated with 1% Triton X-100, and its supernatant fraction was centrifuged on a sucrose step gradient. Phycobilisomes were recovered in the 1 M sucrose band. The phycobilisome fraction was identified by the characteristic appearance of the phycobilisomes, and the absorbance of the component pigments: phycoerythrin, R-phycocyanin, and allophycocyanin Isolated phycobilisomes had a prolate shape, with one particle axis longer than the other. Their size varied somewhat with their integrity, but was about 400-500 A (long axis) by 300-320 A (short axis). Phycobilisome recovery was determined at six phosphate buffer concentrations from 0.067 M to 1.0 M. In 0.5 M phosphate, phycobilisome yield (60%) and preservation were optimal. Such a preparation had a phycoerythrin 545 nm/phycocyanin 620 nm ratio of 8.4. Of the detergents tested (Triton X-100, Tween 80, and sodium deoxycholate), Triton X-100 gave the best results Freezing of the cells caused destruction of phycobilisomes.

Buffers↗
PubMed1971

Chloroplast structure of the Cryptophyceae. Evidence for phycobiliproteins within intrathylakoidal spaces.

Selective extraction and morphological evidence indicate that the phycobiliproteins in three Cryptophyceaen algae (Chroomonas, Rhodomonas, and Cryptomonas) are contained within intrathylakoidal spaces and are not on the stromal side of the lamellae as in the red and blue-green algae. Furthermore, no discrete phycobilisome-type aggregates have thus far been observed in the Cryptophyceae. Structurally, although not necessarily functionally, this is a radical difference. The width of the intrathylakoidal spaces can vary but is generally about 200-300 A. While the thylakoid membranes are usually closely aligned, grana-type fusions do not occur. In Chroomonas these membranes evidence an extensive periodic display with a spacing on the order of 140-160 A. This periodicity is restricted to the membranes and has not been observed in the electron-opaque intrathylakoidal matrix.

Chloroplasts↗
PubMed1969

Properties and Ultrastructure of Phycoerythrin From Porphyridium cruentum.

Phycoerythrin, a photosynthetic accessory pigment, was isolated from Porphyridium cruentum and examined by electron microscopy and disc gel electrophoresis. The absorption monomer, with maxima at 563, 545, and a shoulder at 500 nm, has a molecular weight of about 300,000. With phosphotungstic acid staining it appears as a tightly structured disc-shaped particle possessing a mean diameter of 101 +/- 0.4A and height of 54 +/- 0.7A. The absorption maxima remained the same in glutaraldehyde fixed material, and in dimer and trimer aggregates. Treatment with sodium dodecyl sulfate caused a breakdown into smaller units accompanied by a loss of the 563 nm peak. It is suggested that this absorption monomer is the in vivo functional species and comparable to the phycocyanin hexamer, but structurally distinguishable at the ultrastructural level. It has been calculated that about 35 phycobiliprotein molecules can be contained within each phycobilisome. There are 1.4 x 10(3) chlorophyll molecules per phycobilisome, but not contained within it.

Journal Article↗
PubMed1969

Ultrastructure of blue-green algae.

Two freshwater blue-green algae, Tolypothrix tenuis and Fremyella diplosiphon, and an oscillatorialike marine alga, were found to possess structures on the photosynthetic lamellae which appear to correspond to the phycobilisomes of red algae. These homologous structures are important because they contain the phycobilins which are accessory pigments involved in photosynthesis. As in the red algae, the phycobilisomes were attached on the outer side of each lamellae, i.e., the side facing away from its own membrane pair. Although our study on Anacystis nidulans has not thus far revealed the presence of phycobilisomes, some observations were made on the structure of the polyhedral bodies. After negative staining, the polyhedral bodies were seen to be composed of regularly spaced subunits arranged in a crystalline array. Elongated segmented rods, which differed from the polyhedral bodies, were found in the nuclear region of apparently healthy Tolypothrix cells.

Eukaryota↗
PubMed1968

In vitro Protein Synthesis by Plastids of Phaseolus vulgaris. II. The Probable Relation Between Ribonuclease Insensitive Amino Acid Incorporation and the Presence of Intact Chloroplasts.

Amino acid incorporation into protein by chloroplasts from primary leaves of Phaseolus vulgaris L., var. Black Valentine is only partially inhibited by 400 mug/ml ribonuclease. The rate of incorporation, in the presence of ribonuclease, is progressively inhibited with time, and ceases after about half an hour. Preincubation of chloroplasts at 25 degrees , in the absence of ribonuclease, increases the inhibitory effect of ribonuclease on the initial rate of incorporation of amino acid into protein. Examination of electron micrographs of freshly prepared chloroplast suspensions shows that chloroplasts are largely intact. However, after incubation at 25 degrees for 1 hour the chloroplasts are disrupted, as indicated by loss of their stroma contents. It is concluded that the intact chloroplast membrane is relatively impermeable to ribonuclease. Amino acid incorporating activity probably becomes inhibited as the inside of the chloroplast is made accessible to ribonuclease by breakage of membranes during incubation at 25 degrees .

Journal Article↗
PubMed1966

Granules associated with the chloroplast lamellae of Porphyridium cruentum.

Small granules with a diameter of approximately 350 A are attached to the chloroplast lamellae of the red alga Porphyridium cruentum. To some extent, their size depends on the culture conditions and the age of the cell. It was possible to preserve the granules only with aldehyde prefixation. It can be seen that fixed or negatively stained granules are comprised of smaller subunits. The granules are arranged regularly on the lamellae in repeating rows with a center-to-center granule distance of 400 to 500 A. Attempts at characterization of these chloroplast granules revealed that they are resistant to hydrolysis by ribonuclease and appear to be structurally unaffected by methanol-acetone extraction. Because of their close association with the chloroplast lamellae, they are considered as possible sites of phycobilin concentration. This possibility is supported by two observations: when the phycobilins are removed, the granules disappear; and, when the chlorophyll and stainable membrane portions are selectively removed, the phycobilins and granules are still present. It was found that all other marine red algae examined had granules which were associated with the chloroplast lamellae.

Chloroplasts↗
PubMed1965

The ultrastructure of Porphyridium cruentum.

An electron microscopic examination of Porphyridium cruentum revealed the presence of mitochondria which had been reported absent in this aerobic organism. The chloroplast in this red alga was found to contain small granules (about 320 A) regularly arranged along the parallel chloroplast lamellae. The chloroplast granules differ in size and staining intensity from the ribosomes located in the cytoplasm. Two tubular elements are described. One type (450 to 550 A) is associated with the Golgi bodies. Another type (350 A), in the cell periphery, is believed to connect the endoplasmic reticulum and the cell membrane. Daughter nuclei were found to be positioned at opposite ends of the cell prior to commencement of cell division. Cytokinesis is accomplished by an annular median constriction causing the gradual separation of the chloroplast, pyrenoid, and other cell organelles, resulting in two equal daughter cells. No appreciable differences were observed between cells grown in high light (400 ft-c) and low light (40 ft-c). Structural differences between young and old cells were compared.

Chloroplasts↗