STUDY OF CONFORMATIONAL STABILITY OF DNASE FROM HEPATOPANCREAS OF THECRAB PARALITHODES CAMTSCHATICA

UV and CD spectra of DNase It from crab hepatopancreas were recorded, The number of tyrosine and tryptophan residues in the enzyme was calcu lated using the second derivative of the UV spectrum, The percentage o f canonical secondary structures was calculated using the CD spectrum. The tertiary structure of the enzyme is well developed and its second ary structure is highly ordered and predominantly composed of antipara llel folded beta-sheets. Thermal denaturation was studied by CD spectr oscopy, Crab hepatopancreas DNase K irreversibly denatures at 67 degre es C. This process is cooperative and includes two stages according to the rapid change in the CD spectrum at 70 degrees C and the position of an isodichroic point (210 nm in all spectra at 20-90 degrees C). Ac id-base titration of the enzyme results in partially reversible confor mational changes at pH below 4.0 and above 10.0. This is associated wi th decrease in beta-sheets and increase in beta-coils and unordered st ructures in the secondary structure of DNase K.