Model of the Outer Membrane Potential Generation by the Inner Membrane of Mitochondria

AbstractVoltage-dependent anion channels in the outer mitochondrial membrane are strongly regulated by electrical potential. In this work, one of the possible mechanisms of the outer membrane potential generation is proposed. We suggest that the inner membrane potential may be divided on two resistances in series, the resistance of the contact sites between the inner and outer membranes and the resistance of the voltage-dependent anion channels localized beyond the contacts in the outer membrane. The main principle of the proposed mechanism is illustrated by simplified electric and kinetic models. Computational behavior of the kinetic model shows a restriction of the steady-state metabolite flux through the mitochondrial membranes at relatively high concentration of the external ADP. The flux restriction was caused by a decrease of the voltage across the contact sites and by an increase in the outer membrane potential (up to +60mV) leading to the closure of the voltage-dependent anion channels localized beyond the contact sites. This mechanism suggests that the outer membrane potential may arrest ATP release through the outer membrane beyond the contact sites, thus tightly coordinating mitochondrial metabolism and aerobic glycolysis in tumor and normal proliferating cells

Mg2+ induces intermembrane electron transport by cytochrome c desorption in mitochondria with the ruptured outer membrane

AbstractThe mechanism of external NADH oxidation in rat liver mitochondria is not clear yet, but it evidently includes the intermembrane electron transport (IMET). We showed that Mg2+ significantly stimulated IMET insensitive to rotenone–antimycin A–myxothiazol in mitochondria with the hypotonically damaged outer membrane, even in the absence of exogenous cytochrome c. This effect was more specific than simply ionic strength increase. Direct evidence for cytochrome c desorption from mitochondrial membranes under 4 mM Mg2+ influence was obtained to explain the stimulatory effect of Mg2+ on external NADH oxidation that was coupled to the inner membrane potential generation. Obtained data suggest that cytochrome b5 is normally oriented towards the cytosol in the outer membrane, and can be accessible for endogenous cytochrome c reduction only through the outer membrane rupture or permeabilization, to activate external NADH oxidation

Hemoglobin precipitation by polyethylene glycols leads to underestimation of membrane pore sizes

AbstractThe size of pores formed in the plasma membrane by various substances is frequently determined using polyethylene glycols as osmotic protectants. In this work, we have found that the size of pores formed by saponin in the red blood cell membrane determined by hemolysis versus molecular weight of polyethylene glycol was different to that estimated by light dispersion of cell suspensions. After complete swelling of cells induced by saponin in semiisotonic salt media containing 150 mOsm PEG-4000 or PEG-3000, a significant increase in the light absorbance at 640 nm was developed resulting from the formation of hemoglobin precipitates. Easily sedimenting aggregates were also formed when the supernatant of lysed cells was added to the equiosmotic solutions of polyethylene glycols with molecular weight higher than 1000. We suggest that the real size of large pores could be underestimated due to the phenomenon of hemoglobin precipitation by polyethylene glycols

Improvement of Project Risk Assessment Methods of Implementation of Automated Information Components of Non-commercial Organizational and Technical Systems

The results of a study using the methodological apparatus of the theory of fuzzy logic and automation tools for analyzing input data for risk assessment of projects for the implementation of automated information components of organizational and technical systems are presented. Based on the model of logistics projects for motor transport units, the method for assessing the risks of projects implementing automated information components of non-commercial organizational and technical systems has been improved. To do this, let's analyze the peculiarities of implementing ERP projects as commercial ones and investigate the specifics of the activities of state institutions, when successful tasks, and not economic indicators, lay the foundation for the assessment. It is considered that it is possible to formulate a system of risk assessment indicators for reducing the effectiveness of projects for implementing automated information systems in non-commercial organizational and technical systems. A meaningful interpretation of the fuzzy approach is carried out regarding the formalization of the risk assessment process for projects of automated information systems of public institutions. A tree of fuzzy inference is constructed based on the results of a study of the description of indicators and expert assessments on the risk assessment of the implementation of the project of such an automated information system.The improved method differs from the known ones by the use of hierarchical fuzzy inference, which makes it possible to quantify, reduce the time to evaluate project risks and improve the quality of decisions. An increase in the number of input variables leads to an increase in complexity (an increase in the number of rules) for constructing a fuzzy inference system. The construction of a hierarchical system of fuzzy inference and knowledge bases can reduce complexity (the number of rules). The development of a software module based on the algorithm of the method as part of corporate automated information systems of non-commercial organizational and technical systems will reduce the time for risk assessment of projects for the implementation of automated information systems