Effects of laser (442 and 532 nm) and light-emitting diode (LED) (650 nm) radiation on mitochondrial respiration and mitochondrial electron transport rate (complexes II-III and IV) in the presence of nitric oxide (NO) were investigated. It was found that nitric oxide (300 nM-10 μM) suppresses mitochondrial respiration. Laser irradiation of mitochondria (442 nm, 3 J cm(-2)) partly restored mitochondrial respiration (approximately by 70 %). Irradiation with green laser (532 nm) or red LED (650 nm) in the same dose had no reliable effect. Evaluation of mitochondrial electron transport rate in complexes II-III and IV and effects of nitric oxide demonstrated almost similar sensitivity of complex II-III and IV to NO, with approximately 50 % inhibition at NO concentration of 3 μM. Subsequent laser or LED irradiation (3 J cm(-2)) showed partial recovery of electron transport only in complex IV and only under irradiation with blue light (442 nm). Our results support the hypothesis of the crucial role of cytochrome c oxidase (complex IV) in photoreactivation of mitochondrial respiration suppressed by NO.

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The biological roles of heme and nonheme nitrosyl complexes in physiological and pathophysiological conditions as metabolic key players are considered in this study. Two main physiological functions of protein nitrosyl complexes are discussed—(1) a depot and potential source of free nitric oxide (NO) and (2) a controller of crucial metabolic processes. The first function is realized through the photolysis of nitrosyl complexes (of hemoglobin, cytochrome c, or mitochondrial iron–sulfur proteins). This reaction produces free NO and subsequent events are due to the NO physiological functions. The second function is implemented by the possibility of NO to bind heme and nonheme proteins and produce corresponding nitrosyl complexes. Enzyme nitrosyl complex formation usually results in the inhibition (or enhancement in the case of guanylate cyclase) of its enzymatic activity. Photolysis of protein nitrosyl complexes, in this case, will restore the original enzymatic activity. Thus, cytochrome c acquires peroxidase activity in the presence of anionic phospholipids, and this phenomenon can be assumed as a key step in the programmed cell death. Addition of NO induces the formation of cytochrome c nitrosyl complexes, inhibits its peroxidase activity, and hinders apoptotic reactions. In this case, photolysis of cytochrome c nitrosyl complexes will reactivate cytochrome c peroxidase activity and speed up apoptosis. Control of mitochondrial respiration by NO by formation or photolytic decay of iron–sulfur protein nitrosyl complexes is an effective instrument to modulate mitochondrial metabolism. These questions are under discussion in this study.

Among the photochemical reactions responsible for therapeutic effects of low-power laser radiation, the photolysis of nitrosyl iron complexes of iron-containing proteins is of primary importance. The purpose of the present study was to compare the effects of blue laser radiation on the respiration rate and photolysis of nitrosyl complexes of iron-sulfur clusters (NO-FeS) in mitochondria, subjected to NO as well as the possibility of NO transfer from NO-FeS to hemoglobin. It was shown that mitochondrial respiration in State 3 (V3) and State 4 (V4), according to Chance, dramatically decreased in the presence of 3 mM NO, but laser radiation (λ = 442 nm, 30 J/cm(2)) restored the respiration rates virtually to the initial level. At the same time, electron paramagnetic resonance (EPR) spectra showed that laser irradiation decomposed nitrosyl complexes produced by the addition of NO to mitochondria. EPR signal of nitrosyl complexes of FeS-clusters, formed in the presence of 3 mM NO, was maximal in hypoxic mitochondria, and disappeared in a dose-dependent manner, almost completely at the irradiation dose 120 J/cm(2). EPR measurements showed that the addition of lysed erythrocytes to mitochondria decreased the amount of nitrosyl complexes in iron-sulfur clusters and produced the accumulation of NO-hemoglobin. On the other hand, the addition of lysed erythrocytes to mitochondria, preincubated with nitric oxide, restored mitochondrial respiration rates V3 and V4 to initial levels. We may conclude that there are two possible ways to destroy FeS nitrosyl complexes in mitochondria and recover mitochondrial respiration inhibited by NO: laser irradiation and ample supply of the compounds with high affinity to nitric oxide, including hemoglobin.