Compartmentalization of NaCl in frozen solutions of antifreeze glycoproteins

Effect of high DMSO concentration on albumin during freezing and vitrification

This is a light microscopy image taken of the frozen solution at −20 °C during equilibrium freezing. The freeze concentrate surrounding the ice crystals, comprises unfrozen water and solutes (DMSO and albumin). The bright rectangle is the IR aperture.

In situ spectroscopic quantification of protein-ice interactions

FTIR and confocal Raman microspectroscopy were used to measure interactions between albumin and ice in situ during quasi-equilibrium freezing in dimethyl sulfoxide (DMSO) solutions. At temperatures of -4 and -6 °C, albumin was found to be preferentially excluded from the ice phase during near-equilibrium freezing. This behavior reversed at lower temperatures. Instead, DMSO was preferentially excluded from the ice phase, resulting in an albumin concentration in the freeze-concentrated liquid phase that was lower than predicted. It is hypothesized that this was caused by the albumin in the freeze-concentrated liquid getting adsorbed onto the ice surface or becoming entrapped in the ice phase. It was observed that, under certain freezing protocols, as much as 20% of the albumin in solutions with starting concentrations of 32-53 mg/mL may be adsorbed onto the ice interface or entrapped in the ice phase.

Role of glycopeptides and pepddes in inhibition of crystallization of water in polar fishes

In the ice-laden polar oceans, water temperatures of — 2 °C are common. This temperature is 1.1 °C below the equilibrium freezing point ( — 0.9 °C) of the fishes’ body fluids. Avoidance of freezing in these environments has been linked to the presence of unusual blood peptides and glycopeptides. These molecules have molecular masses ranging from 2.5 to 20 kDa and are viewed as having antifreeze properties because they lower the freezing point of water by a non-colligative process. A 2% solution of antifreeze has a freezing point of — 1.2 °C and ice formed in their presence melts at — 0.02 °C. Measurements of antifreeze concentrations in ice indicate that these molecules, unlike other proteins of similar size and conformation, are incorporated into the solid phase during freezing and adsorb to it. Adsorption of the antifreezes to ice appears to inhibit growth along the preferred axes ( a -axes) by raising the curvature of the growth steps on the basal plane. At temperatures below — 1.2 °C, crystal growth occurs in the form of long spicules whose axes are parallel to the c -axis, the non-preferred axis of growth.

Isopiestic determination of water binding by fish antifreeze glycoproteins

The effectiveness of water binding of antifreeze glycoproteins relative to hemoglobin, cytochrome c and polyvinylpyrrolidone was determined by analyzing results obtained in an isopiestic study at 25 degrees C. The net weight of water which moved from a protein/NaCl aqueous sample to a saturated NaCl reference solution increased in the order: antifreeze glycoprotein, hemoglobin, polyvinylpyrrolidone and cytochrome c. Since the glycoproteins were least effective in transporting water we conclude that, of the proteins studied, the glycoprotein was most effective in binding water under equilibrium conditions at 25 degrees C.

Structure of a peptide antifreeze and mechanism of adsorption to ice

Sequence studies of an alpha-helical peptide antifreeze isolated from winter flounder have revealed the presence of clusters of polar amino acids separated by long sequences of alanine. Most of the polar residues are threonine and aspartate and are separated by 4.5 A, a repeat distance that also separates the oxygens in the ice lattice along the a-axis of an ice crystal. Such a lattice match suggests that the peptide binds to ice by means of hydrogen binding.