Reversible inactivation of soluble liver guanylate cyclase by disulfides

A new amino acid was isolated from the cuticle collagen of $\text{Ascaris lumbricoides}$ and characterized by ultraviolet, mass and nmr spectroscopies and chemical degradation. The results indicate that the compound is an isomer of trityrosine, having an ether linkage. The name “isotrityrosine” is proposed. Its structure suggests that it serves as a crosslink and plays a role in the organization of the collagen structure.     

Myosin in onion (Allium cepa) bulb scale epidermal cells: involvement in dynamics of organelles and endoplasmic reticulum

Studied with the fluorochrome 3,3-dihexyloxacarbocyanine iodide [(DIOC₆(3)], the dynamic system of the endoplasmic reticulum (ER) in epidermal cells of onion bulb scales consists of long, tubular strands moving together with organelles in the deeper cytoplasm, and of a less mobile network composed of tubular and lamellar elements at the cell periphery. Treatment with the sulfhydryl-reagent N-ethylmaleimide (NEM) inhibited organelle and ER movement, and caused the fusion of ER-tubules into flat sheets. Fixed, long, tubular ER strands were formed by lowering the cytosolic pH of NEM-treated cells. Both these observations indicate the involvement of myosin in the dynamics of organelles and ER. Using a monoclonal antibody against murine skeletal muscle myosin (known to cross-react with plant myosin; Tang et al. 1989, J. Cell Sci. 92: 569–574), myosin was identified by immunofluorescence microscopy. Mapping the distribution of myosin, actin filaments, ER, and organelles in different phases of recovery after centrifugation of epidermal cells, co-localization of myosin with ER and organelles but not with actin filaments was observed, supporting the hypothesis that a membrane bound motor protein exists in onion epidermal cells, which translocates organelles and the endoplasmic reticulum along actin filaments.     

Carrier mediated GABA translocation into rat brain mitochondria

GABA added to rat brain mitochondria causes oxidation of intramitochondrial NAD(P)H as well as inducing glutamate efflux from the mitochondrial matrix. The rate of NAD(P)H oxidation shows saturation characteristics, depends on GABA transport across the mitochondrial membrane and is inhibited by non-penetrant compounds and by the metal-complexing agent bathophenanthroline. These results show the existence of a specific GABA carrier. Inhibition studies strongly suggest the existence of two separate binding sites, namely the GABA binding site and the dicarboxylates binding site, as well as suggest the presence of a metal ion (ions) at GABA binding site. The occurrence of a GABA/GLUTAMATE antiport is proposed which allows a cyclical route to account for GABA synthesis and degradation in brain.     

Stimulation of photosynthesis by carbonyl compounds and chelators

A number of carbonyl compounds including bicarbonate, ethylene carbonate, dimethylcarbonate, propylene carbonate, bis-pentamethylene urea, and glycidol, and several chelators were tested for their effect on photosynthetic reactions in isolated spinach chloroplasts. It was found that carbonyl compounds inhibited the DCMU-insensitive silicomolybdate reduction by photosystem II but stimulated the O₂ evolution associated with ferricyanide reduction in presence of DBMIB and the H₂O→methylviologen reaction. Many chelators behaved in the same manner except 1,10-phenanthroline which shows the opposite effect. The carbonyl compounds did not uncouple because they stimulated the proton gradients associated with noncyclic photophosphorylation, whereas some chelators, such as bathocuproine or bathophenanthroline inhibited the proton gradients 100%. Electron transport in presence of ADP and inorganic phosphate showed a stimulation of rates beyond that obtained in presence of an uncoupler. The data are discussed in terms of inhibition of cyclic electron flow around PS II which leads to increased electron transport rates toward PS I.     

The mechanism of energy conservation and transduction by mitochondrial cytochrome c oxidase

Oxidation of ferrocytochrome c by molecular oxygen catalysed by cytochrome c oxidase (cytochrome aa₃) is coupled to translocation of H⁺ ions across the mitochondrial membrane. The proton pump is an intrinsic property of the cytochrome c oxidase complex as revealed by studies with phospholipid vesicles inlayed with the purified enzyme. As the conformation of cytochrome aa₃ is specifically sensitive to the electrochemical proton gradient across the mitochondrial membrane, it is likely that redox energy is primarily conserved as a conformational “strain” in the cytochrome aa₃ complex, followed by relaxation linked to proton translocation. Similar principles of energy conservation and transduction may apply on other respiratory chain complexes and on mitochondrial ATP synthase.     

Segmental flexibility of ribosomal protein S1 bound to ribosomes and Q beta-replicase

The protonization pattern of the endogenous donor component D₁ which feeds electrons directly into chl-a⁺_II has been analyzed in Tris-washed inside-out thylakoids with the aid of appropriate pH-indicators. It was found that under repetitive flash excitation the amount of protons released is proportional to the extent of D₁-oxidation, depending on the time between the flashes. The kinetics of D₁-oxidation (being practically the same as in normal Tris-washed chloroplasts) are faster than the proton release by two orders of magnitude. The results lead to the conclusion that D₁ is protonized in the reduced state with pK(D^ox₁) < 5 and becomes deprotonized in the oxidized state with pK(D^red₁) ? 8. The proton release is kinetically limited by a transport barrier. Implications on the interpretation of the proton release pattern in preparation with intact water oxidation are discussed.     

Inhibition by polyamines of lipid peroxide formation in rat liver microsomes.

Both NADPH- and ascorbic acid-dependent lipid peroxidations were inhibited by spermine, the degree of inhibition being greater with the former peroxidation. The effective concentration of spermine required for inhibition was higher when larger amounts of microsomes were used. However, the activities of NADPH-cytochrome c reductase and NADPH-peroxidase were not influenced by spermine. These results suggest that spermine inhibits lipid peroxidation by binding to phospholipids in the microsomes.     

Carnitine transport in submitochondrial particles and reconstituted proteoliposomes.

Influx and efflux measurements of carnitine with submitochondrial particles lead to the conclusion that carnitine can cross the inner mitochondrial membrane by either facilitated diffusion or more rapidly by a carnitine-carnitine exchange. Both, the facilitated diffusion and the exchange are inhibited by N-ethylmaleimide or mersalyl at low concentrations. Reconstituted particles prepared from liposomes and either submitochondrial particles or an octyl β-glucoside-solubilized preparation were active in catalyzing carnitine-carnitine exchange.