Electron transport chain of Saccharomyces cerevisiae mitochondria is inhibited by H2O2 at succinate-cytochrome c oxidoreductase level without lipid peroxidation involvement.

The deleterious effects of H202 on the electron transport chain of yeast mitochondria and on mitochondrial lipid peroxidation were evaluated. Exposure to H2O2 resulted in inhibition of the oxygen consumption in the uncoupled and phosphorylating states to 69% and 65%, respectively. The effect of H2O2 on the respiratory rate was associated with an inhibition of succinate-ubiquinone and succinate-DCIP oxidoreductase activities.

In spermatozoa, Stat1 is activated during capacitation and the acrosomal reaction.

A role for sperm-specific proteins during the early embryonic development has been suggested by a number of recent studies. However, little is known about the participation of transcription factors in that stage. Here, we show that the signal transducer and activator of transcription 1 (Stat1), but not Stat4, was phosphorylated in response to capacitation and the acrosomal reaction (AR).

In yeast, Ca2+ and octylguanidine interact with porin (VDAC) preventing the mitochondrial permeability transition.

In yeast, Ca(2+) and long chain alkylguanidines interact with mitochondria modulating the opening of the yeast mitochondrial unspecific channel. Mammalians possess a similar structure, the mitochondrial permeability transition pore. The composition of these pores is under debate.

Fluorescence quenching by nucleotides of the plasma membrane H+-ATPase from Kluyveromyces lactis.

The yeast plasma membrane H+-ATPase isolation procedure was improved; a highly pure enzyme (90-95%) was obtained after centrifugation on a trehalose concentration gradient. H+-ATPase kinetics was slightly cooperative: Hill number = 1.5, S0.

F-actin involvement in guinea pig sperm motility.

Sperm motility is a must for natural fertilization to occur. During their travel through the epididymis, mammalian spermatozoa gradually acquire the ability to move. This is accomplished through a sliding movement of the outer doublet microtubules of the axoneme which is energized by the dynein ATPase.

In rat hepatocytes, different adenosine receptor subtypes use different secondary messengers to increase the rate of ureagenesis.

In rat hepatocytes, the role of cAMP and Ca(2+) as secondary messengers in the ureagenic response to stimulation of specific adenosine receptor subtypes was explored. Analyzed receptor subtypes were: A(1), A(2A), A(2B) and A(3). Each receptor subtype was stimulated with a specific agonist while blocking all other receptor subtypes with a battery of specific antagonists.

In guinea pig spermatozoa, the procaine-promoted synchronous acrosome reaction results in highly fertile cells exhibiting normal F-actin distribution.

In guinea pig spermatozoa, procaine induces Ca(2+) independent hyperactivated motility suggestive of sperm capacitation. Nonetheless, in the presence of high extracellular Ca(2+), procaine increases cytoplasmic Ca(2+). We analyze the procaine effect on the acrosome reaction (AR) processes in guinea pig spermatozoa.

Effects of biotin on growth and protein biotinylation in Saccharomyces cerevisiae.

In mammals, biotin, well known for its role as the cofactor of carboxylases, also controls the expression not only of proteins involved in this function, but also of a large number and variety of other different proteins. As a first step towards looking for a rationale for these phenomena, we intend to compare these regulatory functions of biotin between the rat and the much less evolutionized eukaryote, Saccharomyces cerevisiae. Thus far, we have measured growth in yeast cultured on different concentrations of biotin to choose the experimental conditions to be used (2, 200 and 2000 microM) and have found that a band corresponding to the biotinylated S.

Selective herbicide activity of 2,5-di(benzylamine)-p-benzoquinone against the monocot weed Echinochloa crusgalli. An in vivo analysis of photosynthesis and growth.

Six 2,5-diamino-p-benzoquinone derivatives previously characterized as photosystem I electron acceptors were tested for their postemergence herbicide activity. By induction kinetics of chlorophyll a fluorescence performed in vivo it was determined that 2,5-di(benzylamine)-p-benzoquinone diverted electrons at the reducing side of the chloroplast photosystem I. This derivative decreased the efficiency of photosystem II as evidenced by the decrease in the F(v)/F(m) change in Echinochloa crusgalli leaf disks.

Trehalose-enzyme interactions result in structure stabilization and activity inhibition. The role of viscosity.

Stress resistance is essential for survival. The mechanisms of molecule stabilization during stress are of interest for biotechnology, where many enzymes and other biomolecules are increasingly used at high temperatures and/or salt concentrations. Diverse organisms, exhibit rapid synthesis and accumulation of the disaccharide trehalose in response to stress.

Measuring Solution Viscosity and its Effect on Enzyme Activity.

In proteins, some processes require conformational changes involving structural domain diffusion. Among these processes are protein folding, unfolding and enzyme catalysis. During catalysis some enzymes undergo large conformational changes as they progress through the catalytic cycle.

In Saccharomyces cerevisiae, cations control the fate of the energy derived from oxidative metabolism through the opening and closing of the yeast mitochondrial unselective channel.

The yeast mitochondrial unspecific channel (YMUC) sensitivity to inorganic (Ca2+ or Mg2+) or organic (hexyl or octyl-guanidine) cations was measured. The rate of oxygen consumption in State 3 and State 4, the transmembrane potential (deltapsi), mitochondrial swelling, and the polyethylene-glycol mediated recontraction were used to follow opening of the YMUC. Addition of 0.

Closure of the yeast mitochondria unspecific channel (YMUC) unmasks a Mg2+ and quinine sensitive K+ uptake pathway in Saccharomyces cerevisiae.

The K+ uptake pathways in yeast mitochondria are still undefined. Nonetheless, the K+-mediated mitochondrial swelling observed in the absence of phosphate (PO4) and in the presence of a respiratory substrate has led to propose that large K+ movements occur in yeast mitochondria. Thus, the uptake of K+ by isolated yeast mitochondria was evaluated.

Trehalose-mediated inhibition of the plasma membrane H+-ATPase from Kluyveromyces lactis: dependence on viscosity and temperature.

The effect of increasing trehalose concentrations on the kinetics of the plasma membrane H+-ATPase from Kluyveromyces lactis was studied at different temperatures. At 20 degrees C, increasing concentrations of trehalose (0.2 to 0.