Formation of cytochrome c (cyt c)/cardiolipin (CL) peroxidase complex selective towards peroxidation of polyunsaturated CLs is a pre-requisite for mitochondrial membrane permeabilization. Tyrosine residues – via the generation of tyrosyl radicals (Tyr•) - are likely reactive intermediates of the peroxidase cycle leading to CL peroxidation. We used mutants of horse heart cyt c in which each of the four Tyr residues was substituted for Phe and assessed their contribution to the peroxidase catalysis. Tyr67Phe mutation was associated with a partial loss of the oxygenase function of the cyt c/CL complex and the lowest concentration of H2O2-induced Tyr radicals in electron paramagnetic resonance (EPR) spectra. Our MS experiments directly demonstrated decreased production of CL-hydroperoxides (CL-OOH) by Tyr67Phe mutant. Similarly, oxidation of a phenolic substrate, Amplex Red, was affected to a greater extent in Tyr67Phe than in three other mutants. Tyr67Phe mutant exerted high resistance to H2O2-induced oligomerization. Measurements of Tyr fluorescence, hetero-nuclear magnetic resonance (NMR) and computer simulations position Tyr67 in close proximity to the porphyrin ring heme iron and one of the two axial heme-iron ligand residues, Met80. Thus, the highly conserved Tyr67 is a likely electron-donor (radical acceptor) in the oxygenase half-reaction of the cyt c/CL peroxidase complex.

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Geomechanical model construction is an essential part of field development processes planning. Building a correct pore pressure model is one of the key tasks within the process of geomechanical model construction. The traditional approach to pore pressure modeling in oil and gas industry is based on the empirical analytical models usage. This approach has a number of disadvantages, which often lead to the constructed pore pressure model to be incorrect. The authors highlight two most significant disadvantages of the traditional approach: 1) a priori discrepancy between the empirical model and fundamental physical laws; 2) the impossibility of selecting such a combination of parameters of the standard analytical model, for which the resulting pressure corresponds to the entire set of actual field data (pore pressure measurements). This paper proposes a methodology for assessing the pore pressure distribution across the field, based on the usage of neural network technology. This approach potentially eliminates both of the above disadvantages from the pore pressure model building.

This article is continuation of geomechanical estimations for wellbore stability and horizontal wells drilling optimization to M formation of the Boca de Jaruco oilfield, Republic of Cuba. Following the completion of the first part of the work presented in the article SPE-196897-RU, the first horizontal wells were successfully drilled. In the first part of the work, the stress-state analysis and horizontal in-situ stresses directions were analyzed using pressure behavior during steam injections, cross-dipole acoustics, as well as data from oriented caliper from vertical wells. As a result, according to the recommendations, an additional study in the deviated sections of the wells, including core sampling and micro-imager logging were conducted. Presence of wellbore failures at the inclined sections allowed to use the method of inverse in-situ stress modeling based on image logs interpretation. The main result of the work were the determination of the stress state and horizontal stresses direction, as well as classification of the failures detected using the image log into groups. Moreover, the genesis of breakouts which had deviation from each other different that 180° were evaluated.