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K Cain

Publications and source records attributed to K Cain.

62 records · Page 4Linked to original sources
PubMed1977

Dibutylchloromethyltin chloride, a covalent inhibitor of the adenosine triphosphate synthase complex.

1. The synthesis of dibutylchloromethyltin chloride, a new covalent inhibitor of the mitochondrial ATP synthase [oligomycin-sensitive ATPase (adenosine triphosphatase)] complex is described, together with a method for preparing dibutylchloro[(3)H]methyltin chloride. 2. Studies with the yeast mitochondrial oligomycin-sensitive ATPase complex show that dibutylchloromethyltin chloride inhibits both the membrane-bound enzyme and also the purified Triton X-100-dispersed preparation. 3. F(1)-ATPase is not inhibited even at 500nmol of dibutylchloromethyltin chloride/mg of protein, and the general inhibitory properties are similar to those of triethyltin, oligomycin and dicyclohexylcarbodi-imide, known energy-transfer inhibitors of oxidative phosphorylation. 4. Binding studies with yeast submitochondrial particles show that dibutylchloromethyltin chloride antagonizes the binding of triethyl[(113)Sn]tin, indicating that there is an interaction between the two inhibitor-binding sites. 5. Unlike triethyltin, inhibition by dibutylchloromethyltin chloride is due to a covalent interaction which titrates a component of the inner mitochondrial membrane present at a concentration of 8-9nmol/mg of protein. 6. All of the labelled component can be extracted with chloroform/methanol (2:1, v/v), and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of the chloroform/methanol extract indicates that the labelled component has an apparent mol.wt. of 6000-8000. However, t.l.c. reveals the presence of only one labelled component which is lipophilic and non-protein and is distinct from the free inhibitor, mitochondrial phospholipids and the dicyclohexylcarbodi-imide-binding protein (subunit 9). 7. Inhibition of mitochondrial ATPase and oxidative phosphorylation is correlated with specific interaction with a non-protein lipophilic component of the mitochondrial inner membrane which is proposed to be a co-factor or intermediate of oxidative phosphorylation.

Adenosine Triphosphatases↗
PubMed1977

Studies of energy-linked reactions. Inhibition of oxidative phosphorylation by DL-8-methyldihydrolipoate.

1. DL-8-Methyldihydrolipoate was shown to be a potent inhibitor of mitochondrial oxidative phosphorylation and ATP-driven energy-linked reactions. 2. ADP-stimulated respiration utilizing pyruvate + malate and succinate in both ox heart and rat liver mitochondria is inhibited; oxidative phosphorylation using pyruvate + malate, succinate and ascorbate + NNN'N'-tetramethyl-p-phenylenediamine as substrates is also inhibited; uncoupler-stimulated respiration is unaffected regardless of the substrate used. 3. Mitochondrial oligomycin-sensitive adenosine triphosphatase is inhibited in both the membrane-bound form and the purified detergent-dispersed preparation. 4. ATP-driven transhydrogenase and the ATP-driven energy-linked reduction of NAD+ by succinate in ox heart submitochondrial particles are inhibited, whereas the respiratory-chain-driven transhydrogenase is unaffected. 5. DL-8-Methyl-lipoate has no immediate effect on the above reactions, demonstrating the requirement for the reduced form for inhibition. 6. The inhibitory properties of DL-8-methyldihydrolipoate are analogous to those of oligomycin and provide further evidence of a role for lipoic acid in oxidative phosphorylation.

Adenosine Triphosphatases↗
PubMed1977

Studies of energy-linked reactions. Localization of the site of action of trialkyltin in yeast mitochondria.

Ligand-binding studies with labelled triethyltin on yeast mitochondrial membranes showed the presence of high-affinity sites (KD = 0.6 micronM; 1.2 +/- 0.3 nmol/mg of protein) and low-affinity sites (KD less than 45 micronM; 70 +/- 20 nmol/mg of protein). The dissociation constant of the high-affinity site is in good agreement with the concentration of triethyltin required for inhibition of mitochondrial ATPase (adenosine triphosphatase) and oxidative phosphorylation. The high-affinity site is not competed for by oligomycin or venturicidin, indicating that triethyltin reacts at a different site from these inhibitors of oxidative phosphorylation. Fractionation of the mitochondrial membrane shows a specific association of the high-affinity sites with the ATP synthase complex. During purification of ATP synthase (oligomycin-sensitive ATPase) there is a 5-6-fold purification of oligomycin- and triethyltin-sensitive ATPase activity concomitant with a 7-9-fold increase in high-affinity triethyltin-binding sites. The purified yeast oligomycin-sensitive ATPase complex contains approximately six binding sites for triethyltin/mol of enzyme complex. It is concluded that specific triethyltin-binding sites are components of the ATP synthase complex, which accounts for the specific inhibition of ATPase and oxidative phosphorylation by triethyltin.

Adenosine Triphosphatases↗
PubMedDate not supplied

DNA cleavage in rat liver nuclei activated by Mg2+ or Ca2+ + Mg2+ is inhibited by a variety of structurally unrelated inhibitors.

Internucleosomal DNA fragmentation is often regarded as the biochemical hallmark of apoptosis and can be reproduced in vitro in rat liver nuclei. In this study we demonstrate that DNA is initially cleaved into > or = 700, 200-250, and 30-50 kilobase pair (kbp) fragments via a Mg(2+)-dependent, multistep process which can be potentiated by Ca2+. The subsequent internucleosomal cleavage requires both Ca2+ and Mg2+. Furthermore, we show that the heavy metals Cd2+ and Hg2+, dichloroisocoumarin (a general serine protease inhibitor), and N-ethyl maleimide (NEM, a specific thiol reagent) are potent inhibitors of both the Mg(2+)- and Ca2+/Mg(2+)-stimulated DNA fragmentation. In contrast, two other serine protease inhibitors, N-alpha-tosyl-L-lysine chloromethylketone and N-tosyl-L-phenylalanine chloromethylketone are weak and ineffective, respectively, as inhibitors of DNA cleavage. Increasing inhibition of DNA cleavage is accompanied by a shift in the size of the cleaved DNA fragments, which increases from mono- + oligo-nucleosomes-->30-50 kbp-->200-300 kbp--> > or = 700 kbp-->intact DNA. Dithiothreitol, a dithiol, blocks NEM and dichloroisocoumarin inhibition, and since Cd2+ and Hg2+ are also potent--SH blocking agents it is proposed that a critical thiol is involved in the cleavage of DNA into both large kbp fragments and oligonucleosomal-sized fragments.

Animals↗
PubMedDate not supplied

Biochemical mechanisms and morphological selectivity in hepatotoxicity: studies in cultures of hepatic-parenchymal and non-parenchymal cells.

Primary cultures of rat-liver parenchymal and non-parenchymal cells have been used to study some of the factors influencing the selective injury that can be caused in vivo by the direct-acting hepatotoxins beryllium, cadmium, ricin and modeccin to either liver-parenchymal or non-parenchymal cells. The studies on beryllium and cadmium compounds show that it is necessary to consider the chemical species generated in the culture medium, since particulate or colloidal forms are taken up predominantly by non-parenchymal cells whereas soluble forms more readily enter parenchymal cells. The studies with the glycoproteins ricin and modeccin illustrate the importance in their selective cell toxicity of specific membrane-recognition processes present in liver cells, particularly uptake in non-parenchymal cells through interactions with terminal mannose oligosaccharides in the toxins.

Animals↗