قفل کنفورماسیونی و غیر فعال شدن حرارتی آنزیم آمین اکسیداز شیره افوربیا

عنوان انگليسی

Conformational lock and thermal inactivation kinetics of Euphorbia amine oxidase

خلاصه انگلیسی

The kinetics of thermal inactivation of copper-containing amine oxidase from euphorbia latex (ELAO) were studied in a 100-mM sodium phosphate buffer, pH 7, using cadavarine as the substrate. The thermal inactivation curves were not linear at 60-C and 64-C; three linear phases were shown. The first phase gave some information about the number of dimeric forms of the enzyme that were induced by the higher temperatures using the ‘‘conformational lock’’ pertaining theory to oligomeric enzyme. Based on the ‘‘conformational lock’’ theory we estimated that there should be three contact sites between two subunits of ELAO. Since the 3D structure of ELAO has not been determined,we used the X-ray structure of Pea Seedling amine oxidase (PSAO) for determining the contact sites. Alignment of the amino acid sequences of ELAO and PSAO showed that these contact sites are conserved, which are mostly located at the C-terminal region of amine oxidases. The contact sitesare located very near the active site of the enzyme so that it is predictable that destruction of the contact site can lead to inactivation of the enzyme, i.e., the dimeric form is necessary for amine oxidase activity. The second and third phases were interpreted according to a dissociative thermal inactivation model and rate constants of dissociation and denaturation were determined.

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