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Antifreeze glycoproteins: Influence of polymer length and ice crystal habit on activity
Author(s) -
Burcham Timothy S.,
Knauf Michael J.,
Osuga David T.,
Feeney Robert E.,
Yeh Yin
Publication year - 1984
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360230720
Subject(s) - chemistry , ice crystals , supercooling , antifreeze , crystal habit , polymer , antifreeze protein , crystallography , freezing point , crystallization , organic chemistry , biochemistry , thermodynamics , optics , physics
The effect of the ice crystalline habit and the length of the polymer on the ability of the antifreeze glycoproteins (AFGP) from polar fish to depress the freezing temperature of water was investigated. The low‐molecular‐weight components of the glycoproteins, AFGP‐ 6–8, are inactive when a solution of such a sample is nucleated at −6°C. A solution of large AFGP (1–4) is fully functional under the same conditions. The low‐molecular‐weight components differ from the height‐molecular‐weight components in that they contain some proline replacing the alanine in the Ala‐Ala‐Thr · disaccharide polymer unit. In the present experiments, antifreeze activity was examined in the presence of two different forms of ice crystal growth habits, and homodimders of AFGP 6 and 8 were prepared to investigate the function of polymer length and the on antifreeze activity at different degrees of supercooling. The results indicate that the ice crystal growth habit and the introduction of proline into the polymer unit may be responsible for the loss of activity at deep supercooling (−6°C) of AFGP 6–8. The loss in the ability of AFGP to depress the freezing temperature of water at deep supercooling is not solely due to polymer length, as carbodiimide‐linked dimers of AFGP 6 do not function under these freezing conditions. A Model of antifreezing action based on Langmuirian adsorption of AFGP on the ice surface and direct competition between water and AFGP molecules for the incorporation sites in the ice crystal lattice is presented.