Cryoinsolubility of peanut agglutinin. Effect of saccharides and neutral salts.

Peanut agglutinin (PNA) has been shown to be insoluble at low temperatures. This cryoinsolubility has been studied by means of absorption spectroscopy, fluorescence, circular dichroism, and analytical ultracentrifugation. It was found to be dependent on pH, temperature, and protein concentration. No effects on dimer-tetramer equilibrium could be determined nor any conformational changes provoked by exposure of the PNA preparation to low temperatures. The dimer half-molecule apparently does not precipitate. The cryoinsolubility was partially reversible and totally inhibited in the presence of galactosides, the specific ligands of PNA. Their efficacy as inhibitors of cryoinsolubility was related to their affinity for the lectin. The effects of neutral salts and particularly inhibition of the insolubility by strongly chaotropic salts indicate that charge-charge interactions are of little importance and that hydrogen bonds and/or van der Waals interactions are most probably responsible for the formation of the cryoprecipitate.