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Biomedical subjects

R P Casey

Publications and source records attributed to R P Casey.

28 records · Page 2Linked to original sources
PubMed1978

The permeability of the lysosomal membrane to small ions.

The permeability of the lysosomal membrane to small anions and cations was studied at 37 degrees C and pH 7.0 in a lysosomal-mitochondrial fraction isolated from the liver of untreated rats. The extent of osmotic lysis following ion influx was used as a measure of ion permeancy. In order to preserve electroneutrality, anion influx was coupled to an influx of K+ in the presence of valinomycin, and cation influx was coupled to an efflux of H+ using the protonophore 3-tert-butyl-5,2'-dichloro-4'-nitrosalicilylanilide. Lysosomal lysis was monitored by observing the loss of latency of two lysosomal hydrolases. The order of permeability of the lysosomal membrane to anions was found to be SCN- greater than I- greater than CH3COO- greater than Cl- approximately Pi greater than SO24- and that to cations Cs+ greater than K+ greater than Na+ greater than H+. These orders are largely in agreement with the lyotropic series of anions and cations. The implications of these findings for the mechanism by means of which a low intralysosomal pH is produced and maintained are discussed.

Acid Phosphatase↗
PubMed1977

Active proton uptake by chromaffin granules: observation by amine distribution and phosphorus-31 nuclear magnetic resonance techniques.

The hydrogen ion activity within isolated chromaffin granules can be estimated from the distribution of the weak base methylamine and from phosphorus-31 nuclear magnetic resonance spectra of ATP contained in the granules. Following the addition of ATP to the external medium, the internal pH drops by 0.2 to 0.5 unit. This change occurs only in medium containing a permeant anion such as chloride and is abolished by an uncoupler of oxidative phosphorylation. These results indicate that the chromaffin granule membrane possess an electrogenic proton pump directed inward.

Adenosine Triphosphate↗
PubMed1976

Adenosine triphosphate-evoked catecholamine release in chromatin granules. Osmotic lysis as a consequence of proton translocation.

Chromaffin granules suspended in C1-containing media release catecholamine and protein when ATP is added. This phenomenon is inhibited in hyperosmotic media and in the presence of uncouplers of oxidative phosphorylation. Release requires a permeant anion in the medium, but is independent of the cation. The release process appears to be driven by an inwardly directed proton-translocating adenosine triphosphatase. The resulting proton-anion influx causes osmotic lysis of the chromaffin granules.

Adenosine Triphosphate↗
PubMedDate not supplied

What is the essential proton-translocating molecular machinery in cytochrome oxidase?

Pulses of O2 added to anaerobic mitochondria in the presence of antimycin, but in the absence of exogenous reductants, led to H+ translocation until the amount of oxidizing equivalents exceeded the number of endogenous reducing equivalents capable of rapid reduction of cytochrome oxidase. This demonstrates that either the heme of cytochrome alpha or that CuA is the redox center, the function of which is coupled to proton translocation in cytochrome oxidase. Chemical labeling of subunit III of cytochrome oxidase by dicyclocarbodiimide (DCCD), or removal of this subunit by treatment of the enzyme at high pH, results in loss of proton translocation by the isolated and membrane-reconstituted enzyme. Possible roles of subunit III in proton translocation are discussed.

Animals↗
PubMedDate not supplied

Structural and functional alterations induced in the mitochondrial cytochrome b-c1 complex by N,N'-dicyclohexylcarbodiimide.

N,N'-Dicyclohexylcarbodiimide (DCCD) inhibits the activity of ubiquinol-cytochrome c reductase in the isolated and reconstituted mitochondrial cytochrome b-c1 complex. In proteoliposomes containing b-c1 complex DCCD inhibits equally electron flow and proton translocation catalyzed by the enzyme. In both isolated and reconstituted systems the inhibitory effect is accompanied by structural alterations in the polypeptide pattern of the enzyme consistent with cross-linking between subunits V and VII. The kinetics of inhibition of enzymic activity correlates with that of the cross-linking, suggesting that the two phenomena may be coupled. Binding of [14C] DCCD to both isolated and reconstituted enzyme was also observed, though it was not correlated kinetically with the inhibition.

Animals↗