Disruption of flavin homeostasis in isolated rat liver mitochondria.

It has been shown that spontaneous release of non-covalent flavins (from flavoenzymes) begins after isolation of mitochondria from rat liver, which is hydrolyzed to riboflavin. This process is stopped by 1 mM EDTA in the incubation medium. In the presence of NADH, deflavinization of flavoproteins leads to formation of superoxide by at least of three processes. The first of these occurs in complex I as a result of the spontaneous release of FMN from the active center. This process is inhibited by adenosine and guanosine phosphates, as well as NAD, but amplified by nicotinamide. The second process is associated with enzymatic hydrolysis of FAD and FMN to riboflavin; it is blocked by EDTA, AMP, NA, NAD. The third process is associated with non-enzymatic hydrolysis of FAD by iron ions in matrix; it is blocked by EDTA and AMP.

[Tyndall's hypochromism in suspensions].

Since the passage of light through each individual particle in a suspension includes the competition of processes of absorption and scattering, it leads to hypochromism--a decrease in the extinction coefficient. Such "scattering" hypochromism increases with the particle size and its refractive index. Since the Tyndall's light scattering in suspensions, where the size of each particle is substantially larger with respect to wavelengths of light, is not strongly dependent on the wavelength, the absorption spectrum (and excitation spectrum) attenuated almost uniformly at different wavelengths. A simple method to find true extinction coefficients from the absorption (or excitation) spectra of diluted suspensions (not having multiple light scattering) is suggested. The experimental data on spectra of hemoglobin in erythrocytes, actinomycin in DNA and flavins in mitochondria are given.

[Degradation of Mitochondria to Lipofuscin upon Heating and Illumination].

In the present work, it has been shown that the isolated mitochondria can undergo transformation to lipofuscin granules without any additional factors (oxygen saturation, prooxidants). The process occurs spontaneously and slowly at low temperature, and rapidly--by heating (thermo-lipofuscin) or under UV irradiation (photo-lipofuscin). The main contribution to the formation of mitochondrial lipofuscin comes from denatured proteins. Thermo-formation of lipofuscin depends on lipid peroxidation, while the presence of lipids is not required for photo-lipofuscin formation. It is shown that the use of detergent able to degrade mitochondria is necessary to measure lipofuscin content properly.

Stabilization of NADH-dehydrogenase in mitochondria by guanosine phosphates and adenosine phosphates.

It is known that one of the reasons, leading to the development of neuromuscular diseases, including Parkinson's disease, is damage of the mitochondrial NADH-dehydrogenase. Perhaps, it happens when NADH-dehydrogenase loses connection with its coenzyme--flavine mononucleotide (FMN) that occurs at various influences on the enzyme. Previously, we have developed a method, based on fluorescence spectroscopy, to monitor the rate of exit of FMN from isolated mitochondria to solution. Also, we obtained the data that this process is blocked by the enzyme substrate - NADH or by the product - NAD. Recently, we found that this process is strongly blocked by adenine analogs of NAD, contained phosphates: ATP, ADP, and AMP. Adenosine phosphates are able to stabilize the FMN molecule in NADH-dehydrogenase. Using fluorescence spectroscopy and photocolorimetry, we have tested also other natural purine compounds - cAMP, cGMP, GMP, GDP, GTP, IMP, inosine, guanine, and caffeine. It is found that such derivatives of guanine as GMP, GDP, and GTP can prevent the release of FMN into solution. Guanine, cGMP, cAMP and caffeine did not prevent this process. The obtained data allow understand the mechanism of mitochondrial diseases, involving damage of mitochondrial NADH-dehydrogenase, and may help in development of medicines for treatment of these diseases.