CONFORMATION AND IMMUNE ACTIVITY OF ONCOP RECIPITIN CYPREIN

The effect of solution ionic strength, calcium ion concentration, and temperature on spatial structure of cyprein was examined by CD, UV, an d fluorescence spectroscopy. The secondary structure of the cyprein mo lecule was calculated from CD spectra, and the prevalence of the beta- structure (85%) was shown. An irreversible conformational transition i n the range 55-60 degrees C was found, which reduces the binding activ ity of cyprein in interaction with carcinoembryonic antigen (CEA) and anti-cyprein antibodies. In the latter case, the binding activity was reversibly restored. Cyprein was shown to be a calcium-binding protein . Binding of calcium by cyprein and increasing the ionic strength of s olution affect only tertiary structure of the protein. At an ionic str ength of solution close to physiological conditions, calcium-bound cyp rein shows maximum binding to CEA and anti-cyprein antibodies. It was shown by difference UV spectroscopy that cyprein does not interact spe cifically with the monosaccharides of the carbohydrate chains of CEA: fucose, mannose, galactose, and N-acetylglucosamine.