Browsing by Author "Andreeva A."
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Crystallization of type I chloramphenicol acetyltransferase: An approach based on the concept of ionic strength reducers(2000-01-01) Andreeva A.; Borissova B.; Mironova R.; Glykos N.; Kotsifaki D.; Ivanov I.; Krysteva M.; Kokkinidis M.Chloramphenicol acetyltransferase (CAT) is responsible for bacterial resistance to chloramphenicol. It catalyzes inactivation of the antibiotic by acetyl-group transfer from acetyl CoA to one or both hydroxyl groups of chloramphenicol. Type I CAT possesses some unique properties which are not observed in other CAT variants. Type I CAT overexpressed in Escherichia coli was purified and crystals with a resolution limit of 2.22 Å have been obtained using a novel procedure which is based on the concept of 'ionic strength reducers'. The crystals have the symmetry of space group P1 and unit-cell parameters a = 96.46, b = 113.86, c= 114.21 Å, α= 119.9, β= 94.1, γ = 98.6°. These dimensions are consistent with four to six trimers per unit cell, corresponding to a solvent fraction ranging from 65 to 47%.Item Modification of chitosan and possibilities of its application(1995-01-01) Krysteva M.; Naidenova E.; Andreeva A.; Huyen N.D.A modification of amino groups of chitosan were performed in two directions: treatment of vicinal amino and hydroxyl groups by periodate and subsequent interaction with urea and formaldehyde in order of covalent immobilization of enzymes; alkylation of chitosan amino groups for increasing the positive charge and utilization of polymer as an anion exchanger. The binding of enzymes: lipase, trypsin, penicillin amidase and glucose oxidase to the activated matrix was done at pH 4.0, 5.0 and 3.5 respectively. The immobilization of lipase was performed at pH 4.0 and 8.0. The immobilized enzymes were characterized by their pH optimum and relative enzyme activity. The alkylation of the amino groups has been achieved by varying the modifying agent (formaldehyde in the presence of formic acid) to the chitosan. The ion-exchange properties of the ionite obtained was verified by means of ovomucoid, a protein with improved acidic characteristics. © 1995 Taylor & Francis Group, LLC.