In memory of Vladimir Anatolievich Shuvalov (1943-2022): an outstanding biophysicist.

We present here a tribute to one of the foremost biophysicists of our time, Vladimir Anatolievich Shuvalov, who made important contributions in bioenergetics, especially on the primary steps of conversion of light energy into charge-separated states in both anoxygenic and oxygenic photosynthesis. For this, he and his research team exploited pico- and femtosecond transient absorption spectroscopy, photodichroism & circular dichroism spectroscopy, light-induced FTIR (Fourier-transform infrared) spectroscopy, and hole-burning spectroscopy. We remember him for his outstanding leadership and for being a wonderful mentor to many scientists in this area.

The Mechanisms of Electrogenic Reactions in Bacterial Photosynthetic Reaction Centers: Studies in Collaboration with Alexander Konstantinov.

In this review, we discuss our studies conducted in 1985-1988 in collaboration with A. A. Konstantinov, one of the top scientists in the field of membrane bioenergetics.

Analysis of the transformation effect in cytochrome b559 of photosystem II in terms of the model of the heme-quinone redox interaction.

Transformation of three-component redox pattern of cytochrome (Cyt) b559 in PS II membrane fragments upon various treatments is manifested in decrease of the relative content (R) of the high potential (HP) redox form of Cyt b559 and concomitant increase in the fractions of the two lower potential forms. Redox titration of Cyt b559 in different types of PS II membrane preparations was performed and revealed that (1) alteration of redox titration curve of Cyt b559 upon treatment of a sample is not specific to the type of treatment; (2) each value of R defines the individual shape of the redox titration curve; (3) population of Cyt b559 may exist in several stable forms with multicomponent redox pattern: three types of three-component redox pattern and one type of two-component redox pattern as well as in the form with a single E; (4) transformation of Cyt b559 proceeds as successive conversion between the stable forms with multicomponent redox pattern; (5) upon harsh treatments, Cyt b559 abruptly converts into the state with a single E which value is intermediate between the E values of the two lower potential forms. Analysis of the data using the model of Cyt b559-quinone redox interaction revealed that diminution of R in a range from 80 to 10% reflects a shift in redox equilibrium between the heme group of Cyt b559 and the interacting quinone, due to a gradual decrease of 90 mV in E of the heme group at the virtually unchanged E of the quinone component.

Effect of Ca on the redox potential of heme a in cytochrome c oxidase.

Subunit I of cytochrome c oxidase (CcO) from mitochondria and many bacteria contains a cation binding site (CBS) located at the outer positively charged aqueous phase not far from heme a. Binding of Ca with the CBS in bovine CcO inhibits activity of the enzyme 2-3 -fold [Vygodina, T., Kirichenko, A.

Towards an understanding of redox heterogeneity of the photosystem II cytochrome b559 in the native membrane.

A complex redox titration pattern of cytochrome (Cyt) b559 in preparations of thylakoid membranes and photosystem (PS) II membrane fragments is commonly attributed to the presence of three conformational forms differing by a structure of the heme microenvironment. However, despite decades of research, structural determinants underlying differences between the redox forms of Cyt b559 have not been defined. In this work, we propose a different interpretation of redox heterogeneity in the native population of Cyt b559 assuming redox interaction between the Cyt b559 heme group and a nearby bound quinone (Q).

Biphasic reduction of cytochrome b559 by plastoquinol in photosystem II membrane fragments: evidence for two types of cytochrome b559/plastoquinone redox equilibria.

In photosystem II membrane fragments with oxidized cytochrome (Cyt) b559 reduction of Cyt b559 by plastoquinol formed in the membrane pool under illumination and by exogenous decylplastoquinol added in the dark was studied. Reduction of oxidized Cyt b559 by plastoquinols proceeds biphasically comprising a fast component with a rate constant higher than (10s)(-1), named phase I, followed by a slower dark reaction with a rate constant of (2.7min)(-1) at pH6.