[Changes in Na+, K+-ATPase and acetylcholinesterase activity in red cell membranes after freezing-thawing]

The activity of Na+, K+ATPase (EC 3.6.1.3) and acetylcholinesterase (EC 3.1.1.7) as well as the content of masked and exposed SH-groups in sealed and unsealed erythrocyte ghosts were studied as affected by single rapid freezing-thawing. The freezing-thawing procedure resulted in different reactions of membrane-bound enzymes: Na+, K+-ATPase activity is doubled in sealed ghosts and unchanged in unsealed ones. In both types of ghosts the equal decrease in the AChE activity was found to be parallel with the diminution in the content of masked SH-groups but this cannot be referred to exposed SH-groups. The obtained results seem to suggest that the changes in the native conformation of membrane catalytic proteins resulted from cryodamage are responsible for the lowered aChE activity; the primary cause of increase Na+, K+-ATPase activity is due to the changes in the permeability and integrity of erythrocyte membrane, which are followed by the greater accessibility of the substrate (ATP) to the enzyme.