Mitochondrial 1-Cys-peroxiredoxin/thioredoxin system protects manganese-containing superoxide dismutase (Mn-SOD) against inactivation by peroxynitrite in Saccharomyces cerevisiae

Peroxynitrite is a reactive nitrogen species that can mediate protein tyrosine nitration, inactivating many proteins. We show that yeast mitochondrial peroxiredoxin (Prx1p), which belongs to the group 1-Cys-Prx, has thioredoxin-dependent peroxynitrite reductase activity. This activity was characterised in vitro with the recombinant mitochondrial Prx1p, the thioredoxin reductase Trr2p and the thioredoxin Trx3p, using a generator of peroxynitrite (SIN-1). Purified mitochondria from wild-type and null Prx1p or Trx3p yeast strains, exposed to SIN-1, showed a differential inactivation of manganese-containing superoxide dismutase activity. The above yeast strains were exposed to SIN-1 and examined under confocal microscopy. Prx1p or Trx3p-null cells showed a greater accumulation of peroxynitrite than wild-type ones. Our results indicate that this 1-Cys-Prx is a peroxynitrite reductase activity that uses reducing equivalents from NADPH through the mitochondrial thioredoxin system. Therefore, mitochondrial 1-Cys-peroxiredoxin/thioredoxin system constitutes an essential antioxidant defence against oxidative and nitrosative stress in yeast mitochondria.     

Structure of Caribbean coral reef communities across a large gradient of fish biomass

The collapse of Caribbean coral reefs has been attributed in part to historic overfishing, but whether fish assemblages can recover and how such recovery might affect the benthic reef community has not been tested across appropriate scales. We surveyed the biomass of reef communities across a range in fish abundance from 14 to 593 g m⁻², a gradient exceeding that of any previously reported for coral reefs. Increased fish biomass was correlated with an increased proportion of apex predators, which were abundant only inside large marine reserves. Increased herbivorous fish biomass was correlated with a decrease in fleshy algal biomass but corals have not yet recovered.     

Indirect effects of algae on coral: algae-mediated, microbe-induced coral mortality

Declines in coral cover are generally associated with increases in the abundance of fleshy algae. In many cases, it remains unclear whether algae are responsible, directly or indirectly, for coral death or whether they simply settle on dead coral surfaces. Here, we show that algae can indirectly cause coral mortality by enhancing microbial activity via the release of dissolved compounds. When coral and algae were placed in chambers together but separated by a 0.02  μ m filter, corals suffered 100% mortality. With the addition of the broad-spectrum antibiotic ampicillin, mortality was completely prevented. Physiological measurements showed complementary patterns of increasing coral stress with proximity to algae. Our results suggest that as human impacts increase and algae become more abundant on reefs a positive feedback loop may be created whereby compounds released by algae enhance microbial activity on live coral surfaces causing mortality of corals and further algal growth.     

Characterization of chromatin-condensing proteins during spermiogenesis in a neogastropod mollusc (Murex brandaris)

During the process of chromatin cndensation in the spermiogenesis of the neogastropod mollusc Murex brandaris, the nuclear protein complement undergoes a complex series of changes. These changes lead to the appearance of three small protamines in the ripe sperm nuclei. We have characterized this system electrophoretically and at the compositions with antibodies elicited against a specific spermatozoan protamine. Our results indicate that the complex pattern of chromatin condensation during spermiogenesis in this species (M. brandaris) may be modulated by a series of post-translational (and intranuclear) modifications of DNA-interacting proteins, such as precursors to the sperm protamines. The amino acid composition of each sperm protamine is remarkably simple (lys + arg + gly ≥96 mol%). This system of spermiogenic/spermatozoal proteins in the neogastropod M. brandaris clearly differs from that in patellogastropods and archaeogastropods, and it may be helpful in understanding evolutionary changes in the chromatin condensation pattern during the spermiogenesis of gastropod molluscs. © 1994 Wiley-Liss, Inc.     

The regulation of mitochondrial oxygen uptake by redox reactions involving nitric oxide and ubiquinol

The reversible inhibitory effects of nitric oxide (.NO) on mitochondrial cytochrome oxidase and O(2) uptake are dependent on intramitochondrial.NO utilization. This study was aimed at establishing the mitochondrial pathways for.NO utilization that regulate O-(2) generation via reductive and oxidative reactions involving ubiquinol oxidation and peroxynitrite (ONOO(-)) formation. For this purpose, experimental models consisting of intact mitochondria, ubiquinone-depleted/reconstituted submitochondrial particles, and ONOO(-)-supplemented mitochondrial membranes were used. The results obtained from these experimental approaches strongly suggest the occurrence of independent pathways for.NO utilization in mitochondria, which effectively compete with the binding of.NO to cytochrome oxidase, thereby releasing this inhibition and restoring O(2) uptake. The pathways for.NO utilization are discussed in terms of the steady-state levels of.NO and O-(2) and estimated as a function of O(2) tension. These calculations indicate that mitochondrial.NO decays primarily by pathways involving ONOO(-) formation and ubiquinol oxidation and, secondarily, by reversible binding to cytochrome oxidase.     

Effects of hypoxia and thyroid hormone on mRNA levels and activity of phosphoglycerate mutase in rabbit tissues

AIM: In the present work, we studied the effects of hypoxia and triiodothyronine (T(3)) on phosphoglycerate mutase (PGAM) activity and expression in rabbit liver, brain, and skeletal muscle under in vivo conditions. METHODS: Hypoxia was induced in a methacrylate cage with a mixture of 90% nitrogen and 10% oxygen. Hyperthyroidism was induced daily by T(3) injection (250 microg/kg). RESULTS: Hypoxia increases the PGAM activity in liver and brain, tissues which possess type PGAM-BB isozyme, but does not affect the PGAM activity in muscle which possesses type PGAM-MM isozyme. T(3) administration increases the PGAM activity in muscle and liver, but does not affect the enzyme activity in the brain. In all cases, the activity changes in parallel with those of PGAM mRNA levels. CONCLUSION: The tissue-specific effects of hypoxia and T(3) could be explained by the tissue-specific distribution of both PGAM isozyme and T(3) receptors.     

Activation of AMP-dependent protein kinase by hypoxia and hypothermia in the liver of frog Rana perezi

We have investigated different signaling molecules that could be activated by temperature acclimation and hypoxia, using an experimental approach consisting in submerging frogs in a water-filled box maintained at 2-4 degrees C at ambient oxygen levels or supplied with 98% N2:2% CO2 for normoxia or hypoxia conditions, respectively. The results obtained showed no significant changes in the expression of heat shock protein 70. The phosphorylation state of AMP-dependent activated protein kinase, the down-stream component of a protein kinase cascade that acts as an intracellular energy sensor, was significantly increased in both experimental conditions, showing higher values in the absence of oxygen. Similarly, the phosphorylation state of one of its known substrates, elongation factor 2, was also increased, consistent with the arrest of protein synthesis. These results point out an important role of this kinase, adjusting the rates of ATP-consuming and ATP-generating pathways, in the survival strategies to hypoxia and hypothermia.     

The modulation of mitochondrial nitric-oxide synthase activity in rat brain development

Different mitochondrial nitric-oxide synthase (mtNOS) isoforms have been described in rat and mouse tissues, such as liver, thymus, skeletal muscle, and more recently, heart and brain. The modulation of these variants by thyroid status, hypoxia, or gene deficiency opens a broad spectrum of mtNOS-dependent tissue-specific functions. In this study, a new NOS variant is described in rat brain with an M(r) of 144 kDa and mainly localized in the inner mitochondrial membrane. During rat brain maturation, the expression and activity of mtNOS were maximal at the late embryonic stages and early postnatal days followed by a decreased expression in the adult stage (100 +/- 9 versus 19 +/- 2 pmol of [(3)H]citrulline/min/mg of protein, respectively). This temporal pattern was opposite to that of the cytosolic 157-kDa nNOS protein. Mitochondrial redox changes followed the variations in mtNOS activity: mtNOS-dependent production of hydrogen peroxide was maximal in newborns and decreased markedly in the adult stage, thus reflecting the production and utilization of mitochondrial matrix nitric oxide. Moreover, the activity of brain Mn-superoxide dismutase followed a developmental pattern similar to that of mtNOS. Cerebellar granular cells isolated from newborn rats and with high mtNOS activity exhibited maximal proliferation rates, which were decreased by modifying the levels of either hydrogen peroxide or nitric oxide. Altogether, these findings support the notion that a coordinated modulation of mtNOS and Mn-superoxide dismutase contributes to establish the rat brain redox status and participate in the normal physiology of brain development.     

Specific effects of chloride on the photocycle of E194Q and E204Q mutants of bacteriorhodopsin as measured by FTIR spectroscopy

Low-temperature Fourier transform infrared spectroscopy has been used to study mutants of Glu194 and Glu204, two amino acids that are involved in proton release to the extracellular side of bacteriorhodopsin. Difference spectra of films of E194Q, E204Q, E194Q/E204Q, E9Q/E194Q/E204Q, and E9Q/E74Q/E194Q/E204Q at 243, 277, and 293 K and several pH values were obtained by continuous illumination. A specific effect of Cl(-) ions was found for the mutants, promoting a N-like intermediate at alkaline pH and an O' intermediate at neutral or acid pH. The apparent pK(a) of Asp85 in the M intermediate was found to be decreased for E194Q in the presence of Cl(-) (pK(a) of 7.6), but it was unchanged for E204Q, as compared to wild-type. In the absence of Cl(-) (i.e., in the presence of SO(4)(2)(-)), mutation of Glu194 or of Glu204 produces M- (or M(N), M(G))-like intermediates under all of the conditions examined. The absence of N, O, and O' intermediates suggests a long-range effect of the mutation. Furthermore, it is suggested that Cl(-) acts by reaching the interior of the protein, rather than producing surface effects. The effect of low water content was also examined, in the presence of Cl(-). Similar spectra corresponding to the M(1) intermediate were found for dry samples of both mutants, indicating that the effects of the mutations or of Cl(-) ions are confined to the second part of the photocycle. The water O-H stretching data further confirms altered photocycles and the effect of Cl(-) on the accumulation of the N intermediate.     

Acute stress-induced tissue injury in mice: differences between emotional and social stress

Emotional stress affects cellular integrity in many tissues including the heart. Much less is known about the effects of social stress. We studied the effect of emotional (immobilization with or without cold exposure) or social (intermale confrontation) stress in mice. Tissue injury was measured by means of the release of enzyme activities to blood plasma: lactate dehydrogenase (LDH), creatine kinase (CK), aspartate transaminase (AST), and alanine transaminase (ALT). Tape-immobilization increased all these activities in the plasma. AST-ALT ratio was also increased in these animals. Electrophoretic analysis of CK isoenzymes showed the appearance of CK-MB. These results indicate that the heart was injured in immobilized mice. Analysis of LDH isoenzymes and measurement of alpha-hydroxybutyrate dehydrogenase (HBDH) activity suggests that other tissues, in addition to the heart, contribute to the increase in plasma LDH activity. Restraint in small cylinders increased plasma LDH, CK, AST, and ALT activities, but to lower levels than in tape immobilization. Because the decrease in liver glycogen and the increase in plasma epidermal growth factor (EGF) were also smaller in restraint than in the tape-immobilization model of emotional stress, we conclude that the former is a less intense stressor than the latter. Cold exposure during the restraint period altered the early responses to stress (it enhanced liver glycogen decrease, but abolished the increase in plasma EGF concentration). Cold exposure during restraint enhanced heart injury, as revealed by the greater increase in CK and AST activities. Intermale confrontation progressively decreased liver glycogen content. Plasma EGF concentration increased (to near 100 nM from a resting value of 0.1 nM) until 60 minutes, and decreased thereafter. Confrontation also affected cellular integrity in some tissues, as indicated by the rise in plasma LDH activity. However, in this type of stress, the heart appeared to be specifically protected because there was no increase in plasma CK activity, and both AST and ALT increased, but the AST-ALT ratio remained constant. Habituation to restraint (1 h/d, 4 days) made mice resistant to restraint-induced tissue injury as indicated by the lack of an increase in plasma LDH, CK, AST, or ALT activities. Similar general protection against homotypic stress-induced injury was observed in mice habituated to intermale confrontation.