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Biomedical subjects

L Packer

Publications and source records attributed to L Packer.

At least 397 records · Page 22Linked to original sources
PubMed1978

Damage to mitochondrial electron transport and energy coupling by visible light.

The effect of treating mitochondria with visible light above 400 nm on electron transport and coupled reactions was examined. The temporal sequence of changes was: stimulation of respiration coupled to ATP synthesis, a decline in ATP synthesis, inactivation of respiration, increased ATPase activity and, later, loss of the membrane potential. Loss of respiration was principally due to inactivation of dehydrogenases. Of the components of dehydrogenase systems, flavins and quinones were most susceptible to illumination, the iron-sulfur centers were remarkably resistant to being damaged. Succinate dehydrogenase was inactivated before choline and NADH dehydrogenase. Redox reactions of cytochromes and cytochrome c oxidase activity were unaffected. Inactivation was O2-dependent and prevented by anaerobiosis or the presence of substrates for the dehydrogenases. Light in the range 400-500 nm was most effective and the presence of free flavins greatly enhanced inactivation of all of the above mitochondrial activities. This suggests that visible light mediates a flavin-photosensitized reaction that initiates damage involving participation of an activated species of oxygen in the damage propagation.

Animals↗
PubMed1977

Oligomycin-dependent ionophoric protein subunit of mitochondrial adenosinetriphosphatase.

A proteolipid isolated from yeast mitochondrial adenosinetriphosphatase (subunit 9) (ATP phosphohydrolase; EC 3.6.1.3) by chloroform/methanol extraction has been shown to discharge photo-induced potentials across a planar phospholipid membrane containing bacteriorhodopsin. Oligomycin, a specific inhibitor of oxidative phosphorylation which binds to this protein, allows the potential gradient to be reestablished. When proteolipid was isolated from an oligomycin-resistant strain, ionophoric activity was still obtained but the effect was not reversed by oligomycin. These studies suggest that the hydrophobic subunit-9 polypeptide is the ionophoric component linking ATP synthesis (hydrolysis) with proton translocation.

Adenosine Triphosphatases↗
PubMed1977

Surface localization of sites of reduction of nitroxide spin-labeled molecules in mitochondria.

The relative rates of reduction of several spin-labeled molecules that partition differently across the hy-drophobic-interface of inner membranes from rat liver mitochondria were investigated. Spin labels localized either deep in the hydrophobic region or in the aqueous phase are only slowly reduced; however a spin-labeled analogue of the cationic detergent cetyltrimethylammonium bromide that partitions at the interface is rapidly reduced by coupled electron transport. Chemical studies on the reduction and oxidation of the spin label show that loss of signal is due to reduction and not destruction of the label. No evidence was found for flip-flop of the label in submitochondrial preparations. Spin reduction of respiring mitochondria, mitoplasts, or inverted submitochondrial preparations is inhibited by rotenone but is relatively insensitive to antimycin A and KCN. Because the midpoint potentials of the spin labels were found to be similar to that of ubiquinone, it is concluded that reducing equivalents of mitochondrial electron transport from this region of the chain are channeled to either membrane interface.

Aerobiosis↗
PubMed1977

Extension of the lifespan of cultured normal human diploid cells by vitamin E: a reevaluation.

Previously we reported [Packer, L. & Smith, J.R. (1974) Proc. Natl. Acad. Sci. USA 71, 4763-4767] that the lifespan of WI-38 human diploid fibroblasts in vitro was significantly increased by continuously growing the cell cultures in the presence of vitamin E(dl-alpha-tocopherol), but in 19 subsequent subcultivation series we were unable to reproduce these findings. While vitamin E is incorporated into the cells and is able to act effectively as an antioxidant, apparantly is intracellular antioxidant properties alone do not routinely result in an increase of cell lifespan. A synergism between vitamin E and some component(s) in the first of two lots of serum used in the original experiments seems the most likely explanation for our earlier findings.

Cell Division↗