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Biomedical subjects

W L Butler

Publications and source records attributed to W L Butler.

At least 55 records · Page 3Linked to original sources
PubMed1975

Spectral Characterization of the Photoreducible b-Type Cytochrome of Dictyostelium discoideum.

Irradiation of a soluble extract from broken cells of Dictyostelium discoideum causes the photoreduction of a b-type cytochrome. The cytochrome b can be separated from cytochrome c, which is also present in the extract, by column chromatography on Brushite, but the cytochrome b is no longer sensitive to light after separation on the column. Low temperature spectroscopy shows that reduced form of the photoreducible cytochrome b has a Soret band at 423 nm and a split alpha band with maxima at 558 and 551 nm similar to the b-type cytochrome in complex II of beef heart mitochondria.

Journal Article↗
PubMed1973

Light-induced absorbance changes associated with phototaxis in Dictyostelium.

Reversible light-induced absorbance changes were observed in the phototactic organism Dictyostelium discoideum. Irradiation of cells with light in the 520- to 600-nm region results in an absorbance increase at 411 nm, which decays in darkness with a half-time of about 7 sec. A similar light-induced absorbance change was observed in a 12,000 x g pellet of a cell-free homogenate and in a soluble fraction obtained after sonication of the 12,000 x g pellet. Dithionite had to be added to the cell-free extracts in order for the light-induced change to decay in darkness. The absorbance change was maximally elicited by light in the region of 560 nm. A similar spectral sensitivity was found for the phototactic migration of the pseudoplasmodia. The agreement between the spectral sensitivities of the two processes suggests that the absorbance change is associated with phototaxis.

Cell-Free System↗
PubMed1972

The relationship between P-680 and C-550.

The published reports of flash-induced absorbance changes in the 680-690 nm spectral region, which have been attributed to bleaching of the primary reaction center chlorophyll of photosystem II (PSII) P-680, are discussed in light of what is known about the primary electron acceptor of PSII, C-550. The question of whether the fluorescence yield changes, which accompany the photoreduction of C-550, might influence the measurements of chlorophyll bleaching is examined. The responses attributed to P-680 and their relationship to C-550 indicate that, if the absorbance measurements are valid, P-680 probably functions as the primary electron donor to PSII rather than as a photochemical sensitizer of the primary redox reaction.

Alkanes↗