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A W FRENKEL

Publications and source records attributed to A W FRENKEL.

9 recordsLinked to original sources
PubMed1965

OBSERVATIONS ON THE STRUCTURE OF RHODOSPIRILLUM MOLISCHIANUM.

The lamellae of the bacterium Rhodospirillum molischianum originate as extensions of the cytoplasmic membrane into the cytoplasm of the cell. Initially, these extensions are narrow folds and occur independently of one another. The first lamellae to appear average about 80 A in width, representing one side of the infolded cytoplasmic membrane, or 160 A when the two sides of the fold are closely appressed. The 160-A lamellae increase in number and may associate to form larger lamellae, which represent varying degrees of association between adjacent folds. Later, the space within each fold increases; the two appressed regions of the cytoplasmic membrane in each fold separate to form distinct invaginations, and the lamellae observed at this stage are formed by an association of the sides of adjacent invaginations.

Cell Membrane↗
PubMed1965

OBSERVATIONS ON THE STRUCTURE OF RHODOSPIRILLUM RUBUM.

Sections of Rhodospirillum rubrum cells from cultures of different ages have been examined to obtain information on the development of chromatophores in this organism. Cells from the 12-hour cultures studied contain neither distinct invaginations of the cytoplasmic membrane nor distinct chromatophores. The first structures that can be related to chromatophore development occur peripherally in the cells, are relatively few in number, relatively high in density, and have an indistinct membrane. In cells from 26-hour cultures numerous distinct invaginations of the cytoplasmic membrane are present, and all layers of the cytoplasmic membrane are involved in the formation of each invagination. As the invaginations become more numerous, the ends of the invaginations become constricted to form one or more structures similar to the chromatophores previously described in this organism. Cells of R. rubrum, therefore, develop a structural continuum which initially consists of invaginations of the cytoplasmic membrane, and later of the chromatophores produced by and attached to these invaginations. The presence of this continuum, however, does not necessarily exclude the existence of discrete chromatophores within these cells. Several other structures previously reported in this organism are described in greater detail.

Cell Membrane↗
PubMed1959

The structure of Rhodospirillum rubrum.

Cells from serial cultures of R. rubrum, grown anaerobically in the light, were harvested at intervals from (1/2) to 15 days and sectioned for electron microscopy by conventional methods. Cells of this species possess a multilayered outer envelope, and the external cell surface is differentiated into ridges extending parallel or obliquely to the long axis of the cell. Cells from very young cultures resemble non-photosynthetic bacteria and contain only a granular cytoplasm, scattered high-density particles, and low-density areas corresponding to the chromatin areas observed by light microscopy. They contain neither the chromatophores nor the lamellar systems assumed by previous investigators to be characteristic of this species when grown anaerobically in the light. Chromatophores appear in cells from cultures older than about 12 hours, while systems of paired lamellae appear along with the chromatophores in cells from cultures older than about 8 days. Divergent opinions concerning the occurrence of chromatophores or lamellae in this species can be resolved on the basis of the age of cultures used in previous studies. Other changes occurring in cells from cultures of increasing age include the appearance of granular and reticulate cytoplasmic bodies and vacuoles, extension of the chromatin areas, and the appearance of a single membrane enclosing several chromatophores.

Cell Membrane↗
PubMed1959

Structure and photochemical activity of chlorophyll-containing particles from Rhodospirillum rubrum.

Comparative studies on isolated chromatophores and on sectioned cells of the photosynthetic bacterium Rhodospirillum rubrum confirm the assumption expressed in earlier investigations that the photochemically active chromatophores isolated from disrupted cells represent structural chlorophyll-bearing components of the protoplast. Actively growing cells from light-grown cultures about 12 hours old do not release chromatophores when disrupted in dilute buffers, but do release smaller, chlorophyll-containing structures about 25 mmicro in diameter. Sections of such cells do not reveal chromatophores, but contain in the ground cytoplasm numerous particles somewhat smaller in size than the 25 mmicro chlorophyll-containing particles released from disrupted cells. Similar particles are obtained by the sonication of isolated chromatophores obtained from cells of 1-day-old cultures. The small, subchromatophore particles described here appear to be functionally complete units which are photochemically active in photo-oxidation, photoreduction, and photophosphorylation, and it is postulated that they represent the basic biochemical and structural components of the chromatophore.

Chlorophyll↗
PubMed1953

Photosynthesis.

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Photosynthesis↗