Béla Somogyi

The effect of transmembrane potential on the dynamic behavior of cell membranes

The relationship between transmembrane potential and lipid dynamics in the cytoplasmic membrane of mouse thymus cells has been investigated. Changes of transmembrane potential was followed by measuring the fluorescence emission of the anionic dye, bis-(1,3-dibutylbarbiturate)trimethine oxonol (diBa-C4-(3)). Assessment of lipid fluidity was carried out applying three fluorescent lipid probes, 1-[4-(trimethylammonium)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH), 12-(9-anthroyloxy)stearic acid (12-AS) and 1,6-diphenyl-1,3,5-hexatriene (DPH) used to monitor different structural regions of the bilayer. The fluorescence anisotropy of these probes was measured as a function of temperature at two values of transmembrane potential. In the case of DPH it proved to depend on the membrane potential in the higher temperature range (above 28 degrees C), while no such a dependence could be observed for DPH below this temperature range and for TMA-DPH and 12-AS in between 20 and 37 degrees C. These data suggest that changes in transmembrane potential are accompanied with some local alteration in membrane lipid dynamics and/or structure.

The effect of viscosity on the apparent decomposition rate on enzyme-ligand complexes

Abstract A theoretical model is presented for describing a previously untreated effect of viscosity on the apparent decomposition rate of enzyme-ligand complexes. Since the translational diffusion is hindered by the viscosity, its increased value results in an enlarged portion of ligands which can be rebound by the enzyme immediately after the dissociation of the complex. The model accounts for the experimentally observed decrease in maximal velocity of enzymic reactions at high viscosity. At the same time, it serves as a tool to obtain new information about the energetic processes of enzyme action.

Protein dynamics and function

Abstract A brief overview is presented where the principal question is the possible contribution of protein dynamics to biological function. First the molecular enzyme kinetic model of the authors is presented, where the involvement of the mass-distribution of solvent-solute particles and of the environmental viscosity in enzyme action and regulation is outlined. Further subtitles deal with the functional role of dynamic displacement of cell membrane proteins, their relative proximity and the fluorescence methods for monitoring them, with special attention to that which was developed by the authors (flow cytometric energy transfer).

Physical analysis of the molecular motions during transcription

Abstract A simple theoretical model is presented dealing with the mechanical motion of the bacterial DNA-dependent RNA polymerase during transcription. Derivation of a physical model, based on accepting the existence of a series of Michaelian-type complexes during the transcription, resulted in a contradiction with physical reality. In order to solve this energetic contradiction, a model is suggested regarding the polymerase as an elastic, fluctuating entity instead of a quasi-rigid sphere.

Dynamic interaction between functional groups in the active site of glycogen phosphorylase b

The quenching of coenzyme fluorescence in glycogen phosphorylase b is reinvestigated. Data with anionic quenchers show deviations from the original Stern-Volmer kinetics. A kinetic analysis based on measured lifetime data indicates a collisional quenching process, which is, however, not diffusion-controlled. It is proposed, that the quenching takes place primarily by enzyme-bound quencher species. The observed inhibition of the enzyme reaction by I- and IO-3 is consistent with this hypothesis. The inhibition pattern and spectral investigation refer to a true competition with the substrate, glucose-1-phosphate. So, this dynamic quenching can be regarded as an indicator of rapid conformational fluctuations which bring the two important active-site groups in contact. Effect of ligand binding on the quenching of coenzyme fluorescence should also be revaluated according to these results.

STRUCTURE AND DYNAMICS AT MOLECULAR AND CELLULAR LEVELS

Publisher Summary This chapter focuses on structure and dynamics at the molecular and cellular levels. Molecular and cellular events take place in a certain time period and space. The translational and rotational diffusion coefficients are inversely related to the diameter of spheric molecules. The latter has a relationship also with the minus third power of the diameter. Thus, it can be stated that the smaller the molecule, the faster the motion that can be observed at a certain temperature. A similar rule is valid for the vibrational motions of different groups of macromolecules. Since the early experimental approach of Linderstrom–Lang, many attempts have been made to follow the dynamics of molecular and cellular events. The available physical methods are also confined to time intervals; therefore, to study a particular type of motion, a method having the right correlation time needs to be selected. This chapter presents the Lineweaver–Burk plot of the activity of phosphorylase b . It also describes the time kinetics of fluorescein diacetic acid hydrolysis of normal mouse lymphocytes at different osmolality levels.