Miroslav Živić

Investigation of the radical scavenging potency of hydroxybenzoic acids and their carboxylate anions

In this article, the antoxidative mechanisms HAT, SPLET, and SET-PT of the ortho-, meta-, and para-hydroxybenzoic acids and corresponding carboxylate anions with different radicals (·OO−, ·OH, ·OOH, and CH3OO·) were investigated. For this reason, the ΔHBDE, ΔHIP, and ΔHPA values of the corresponding reactions in different solvents (water, DMSO, pentylethanoate, and benzene) were examined. For this purpose, the M05-2X/6-311++G(d,p) and B3LYP-D2/6-311++G(d,p) theoretical models were applied. Although the B3LYP-D2 method produced lower reaction enthalpy values, both theoretical models exhibited the same trend. It was found that SET-PT is not a favorable reaction path for any hydroxybenzoic acids and their anions with any radicals in any solvents. No anion reacts with −·O2, whereas meta- and para-hydroxybenzoic acids react with −·O2 only in nonpolar solvents. In all other cases, the HAT and SPLET mechanisms are competitive. Which of them is dominant depends on the properties of the acids, anions, radicals, and solvents.Graphical Abstract

The interactions of vanadium with Phycomyces blakesleeanus mycelium: enzymatic reduction, transport and metabolic effects

The biological and chemical basis of vanadium action and transport in fungi is relatively poorly understood. In this study we investigated the interactions of vanadium in physiologically-relevant redox states: vanadate (+5) and vanadyl (+4), with mycelium of fungus Phycomyces blakesleeanus using EPR and (31)P NMR spectroscopy and biochemical assays. We determined that P. blakesleeanus reduces V(5+) to V(4+) in the extracellular compartment by the means of cell surface enzyme with ferricyanide reductase activity, which contains molybdenum-molybdopterin as a cofactor. Both, V(5+) and V(4+) bind to cell wall. They enter the cytoplasm via phosphate transporter and cation channels, respectively, and exhibit different metabolic effects. Vanadate provokes increased biomass production, the effects being inverted to toxic at higher V(5+) concentrations. In addition, V(5+) activates the synthesis of sugar phosphates and oligophosphates. On the other hand, V(4+) exhibits toxic effects even at low concentrations. The V(4+) detoxification route involves binding to vacuolar polyphosphates. Altogether our results imply that the mechanism of interaction of vanadium with P. blakesleeanus involves three major steps: extracellular enzymatic V(5+)/V(4+) reduction, V(4+) influx, and vacuolar storage, with an additional step - V(5+) import occurring at higher vanadate concentrations.

Oxygen regulation of alternative respiration in fungus Phycomyces blakesleeanus: connection with phosphate metabolism

Environmental changes can often result in oxygen deficiency which influences cellular energy metabolism, but such effects have been insufficiently studied in fungi. The effects of oxygen deprivation on respiration and phosphate metabolites in Phycomyces blakesleeanus were investigated by oxygen electrode and (31)P NMR spectroscopy. Mycelium was incubated in hypoxic and anoxic conditions for 1.5, 3 and 5 h and then reoxygenated. Participation of alternative oxidase (AOX) in total respiration increased gradually in both treatments and after 5 h of anoxia exceeded a value 50% higher than in control. Shortly after reintroduction of oxygen into the system AOX level decreased close to the control level. Oxygen deprivation also caused a reversible decrease of polyphosphate/inorganic phosphate ratio (PPc/Pi), which was strongly correlated with the increase of AOX participation in total respiration. Unexpectedly, ATP content remained almost constant, probably due to the ability of PolyP to sustain energy and phosphate homeostasis of the cell under stress conditions. This was further substantiated by the effects of azide, a cytochrome c oxidase inhibitor, which also decreased PPc/Pi ratio, but to a smaller extent in oxygen deprived than control and reoxygenated specimens.

Vanadate Influence on Metabolism of Sugar Phosphates in Fungus Phycomyces blakesleeanus

The biological and chemical basis of vanadium action in fungi is relatively poorly understood. In the present study, we investigate the influence of vanadate (V5+) on phosphate metabolism of Phycomyces blakesleeanus. Addition of V5+ caused increase of sugar phosphates signal intensities in 31P NMR spectra in vivo. HPLC analysis of mycelial phosphate extracts demonstrated increased concentrations of glucose 6 phosphate, fructose 6 phosphate, fructose 1, 6 phosphate and glucose 1 phosphate after V5+ treatment. Influence of V5+ on the levels of fructose 2, 6 phosphate, glucosamine 6 phosphate and glucose 1, 6 phosphate (HPLC), and polyphosphates, UDPG and ATP (31P NMR) was also established. Increase of sugar phosphates content was not observed after addition of vanadyl (V4+), indicating that only vanadate influences its metabolism. Obtained results from in vivo experiments indicate catalytic/inhibitory vanadate action on enzymes involved in reactions of glycolysis and glycogenesis i.e., phosphoglucomutase, phosphofructokinase and glycogen phosphorylase in filamentous fungi.

Alternative respiration of fungus Phycomyces blakesleeanus.

Respiratory characteristics of germinating spores, developing mycelium and mitochondria of the fungus Phycomyces blakesleeanus were investigated by means of oxygen Clark-type electrode. The effects of respiratory inhibitors and metabolic compounds on oxygen consumption were tested. It was demonstrated that P. blakesleeanus apart of cyanide-sensitive respiration, CSR, possess alternative respiration, (cyanide-resistant respiration, CRR) which is constitutive and whose capacity decreases during development. Maximum is observed for activated spores where CRR capacity is significantly greater than CSR. After treatment with antimycin A, a third type of respiration insensitive to antimycin A and low concentration of SHAM (sufficient for inhibition of CRR), but sensitive to cyanide and high concentration of SHAM, has been expressed.

Outwardly Rectifying Anionic Channel from the Plasma Membrane of the Fungus Phycomyces blakesleeanus

ABSTRACT In the present report, by using a patch clamp technique, we provide, to our knowledge, the first detailed description of an anionic channel from filamentous fungi. The characterized channel, an outwardly rectifying anionic channel (ORAC), is the most prominent feature of the cell membrane of the fungus Phycomyces blakesleeanus in the absence of energizing substrates. The unitary conductance of the channel is 11.3 ± 0.4 pS. It is characterized by a strong voltage dependence of the open-channel probability (zδ; the gating charge is 2.1 ± 0.1), and the channel is activated by depolarization. The values of the time constants for voltage-induced activation and deactivation of 28 ± 3 ms for τa and 39 ± 9 ms for τd show that the ORAC is characterized by fast activation/deactivation kinetics. The ORAC shows strong selectivity for anions over cations and weak selectivity among anions, with a selectivity sequence of I− ≥ NO3− > Br− > Cl− > SO42− = 4.8 > 4.4 > 2.2 > 1 > 0.55, which corresponds to Eisenman series 1. The channel is characterized by two open and two closed states, with dominant long open (τo2 = 35.0 ± 3.9 ms) and long closed (τc2 = 166 ± 28 ms) states occupying 63% ± 8% and 79% ± 3% of total open and closed times, respectively. The ORAC is insensitive to anthracene-9-carboxylic acid (<200 μM), but 2 mM malate reversibly inhibits 59% ± 12% of the channel activity. Based on the electrophysiological properties of the channel, we propose that the ORAC plays a role in anion accumulation and in membrane potential regulation through local membrane depolarization.

A New Model System for Investigation of Ionic Channels in Filamentous Fungi: Evidence for Existence of Two K+-Permeable Ionic Channels in Phycomyces blakesleeanus

Abstract: A technique was developed to obtain viable cytoplasmic droplets, enabling the formation of a gigaohm seal. Such cytoplasmic droplets can be used for characterization of plasma membrane ion channels from filamentous fungi by patch‐clamp technique. Two K+ ionic channels are characterized with a conductance of 43 pS and 74 pS.

Evaluation of oxidative stress biomarkers in the freshwater gammarid Gammarus dulensis exposed to trout farm outputs

The current study reports a combined seasonal monitoring of the Crnica River watercourse using physico-chemical parameters and biomarkers measured in Gammarus dulensis with the aim of correlating the effects of pollution with the level of oxidative stress biomarkers in this amphipod. The pollution source is identified as a trout farm in the upper part of the Crnica River (Eastern Serbia). Physico-chemical water parameters and sediment trace element concentrations were measured in the Crnica River during three seasons. Three localities downstream [CR2, CR3, and CR4 (20 m, 400 m, and 1.3 km from the trout farm discharge, respectively)] were assessed in comparison with a reference location (CR1), 250 m upstream from the trout aquaculture in the Crnica River. Antioxidant biomarkers including the enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR), and glutathione-S-transferase (GST) were determined in pooled samples of G. dulensis. Our findings showed statistically different antioxidant enzyme levels in gammarids from the first downstream locality (CR2) compared to those from other three localities. The results indicate that oxidative stress occurred to some extent despite the assumed antioxidant induction as a result of exposure to elevated levels of some elements and changed water parameters, the effects seeming in part to be mediated by suppression of SOD and CAT (during summer and autumn); and by suppression of GPX and GR (during autumn) at the CR2 locality. The activity of GST in all seasons was higher at the CR2 locality than at the other localities, suggesting the presence of some permanent xenobiotic next to the aquaculture output. Seasonal difference in the physical and chemical water parameters and sediment trace element concentrations were observed. Overall, our results indicate a locality- and season-dependent antioxidant enzymes response in G. dulensis, pointing at progressively reduced deleterious effect of trout farm outputs with movement further downstream.

Osmotic swelling activates a novel anionic current with VRAC-like properties in a cytoplasmic droplet membrane from Phycomyces blakesleeanus sporangiophores.

We describe here whole-cell currents of droplets prepared from the apical region of growing Phycomyces blakesleeanus sporangiophores. Whole-cell current recordings revealed the osmotically activated, outwardly rectifying, fast inactivating instantaneous current (ORIC) with biophysical properties closely resembling volume-regulated anionic current (VRAC). ORIC is activated under conditions of osmotically induced swelling and shows strong selectivity for anions over cations. In addition, ORIC shows voltage and time-dependent inactivation at positive potentials and recovery from inactivation at negative potentials. ORIC is blocked by anthracene-9-carboxylic acid, an anion channel blocker, in a voltage-dependent manner. This is the first report of the presence of VRAC-like current in an organism outside the chordate lineage.

Ithytrichia Eaton, 1873 (Hydroptilidae: Trichoptera): A Genus New for the Entomofauna of Serbia

ABSTRACT: During field work carried out in 2003, 2004, 2007, and 2011, larvae of the genus Ithytrichia (Trichoptera, Hydroptilidae) were identified as part of a benthic macroinvertebrate survey. Specimens of Ithytrichia lamellaris Eaton, 1873 were collected from independent localities in four rivers of Eastern and Central Serbia, namely the Black Timok, Mlava, Morava, and Western Morava. For the fauna of Serbia, three species within the family Hydroptililae were known up to now: Hydroptila vectis, Hydroptila sparsa, and Agraylea multipunctata. This is the first record of Ithytrichia larvae in watercourses of Serbia (Danube basin). Analysis of the environmental data indicates that I. lamellaris is a typical eurythermic species which inhabits slightly alkaline waters rich in dissolved oxygen, with a moderate organic load and abundant aquatic vegetation.