Ice-active proteins from the Antarctic nematode Panagrolaimus davidi.

The Antarctic nematode Panagrolaimus davidi has an ice-active protein that shows recrystallization inhibition but no thermal hysteresis. It belongs to a class of ice-active proteins found in a variety of freezing-tolerant organisms that display insignificant levels of thermal hysteresis in the context of the environmental temperatures to which they are exposed. The recrystallization inhibition activity of the P. davidi ice-active protein is present at low concentrations, is relatively heat stable, is affected more by acid than by alkaline pH, is not calcium dependant and is not affected by reagents that target carbohydrate residues or sulphydryl linkages. A hexagonal ice crystal growth form also indicates the presence of an ice-active protein. This protein could have important functions in the survival of intracellular freezing by this organism by controlling the stability of ice after its formation.