Kam Nedev

KN Nedev, IU Khurgin
The surface of the alpha-chymotrypsin globule is investigated using a three-dimensional model of the molecule, constructed on the basis of X-ray data by sectioning the space of the protein globule in cubic elements with a step of 3 A. The surface layer contains about 55% of the overall globule volume. The atomic density of so defined surface was found to be approximately equal to that in the inner part of the globule. Topographical maps of the alpha-chymotrypsin surface were drawn and an analysis of the distribution of polar and unpolar atoms and groups on the surface and in the inner part of the globule was carried out. Some conclusions drawn from the atomic density, energetic and structural heterogeneity of the surface and concerning the conformational integrity and functional activity of alpha-chymotrypsin molecule are presented. Some aspects of the protein hydration problem are discussed and a structural model of the alpha-chymotrypsin hydratation shell is proposed, the main features of which are amorphism and the lack of long-range effect on the structure of water around the hydrated protein globule.

KN Nedev, RI Volkova, YI Khurgin, DS Chernavskii
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Nedev KN
The distribution of atomic density in the elastase and subtilysin globulas was modeled on the basis of their x-ray atomic coordinates and was consequently investigated through comparison with the normal Poisson distribution, using the chi2-test. The results from the above procedure are discussed in connection with the concept of kinetic constraints on the globula folding process as well as with the enzyme-machine hypothesis. It is shown that the minimum average dimensions of atomic irregularities in the protein globula are about 200 A3.

Roumiana Todorova, Kamen Nedev
The effect of the low-molecular-mass natural reagents in high concentrations is important for investigating enzymatic reactions in near "in vivo" conditions and for optimisation of biotechnology processes. A model system, including p-nitrophenyl acetate as substrate and alpha-chymotrypsin as proteolytic enzyme, has been used to study the effect of high concentrations of sucrose, both influencing the viscosity of the reaction medium and acting as a nucleophilic effector (activator) on the enzymatic reaction. A kinetic scheme at high concentrations of nucleophilic effectors (sucrose) has been proposed.

Nedev KN
The distribution of atomic density in the elastase and subtilysin globulas was modeled on the basis of their x-ray atomic coordinates and was consequently investigated through comparison with the normal Poisson distribution, using the chi2-test. The results from the above procedure are discussed in connection with the concept of kinetic constraints on the globula folding process as well as with the enzyme-machine hypothesis. It is shown that the minimum average dimensions of atomic irregularities in the protein globula are about 200 A3.