J. Biol. Chem., Vol. 261, Issue 14, 6390-6397, 05, 1986
A kinetic description of antifreeze glycoprotein activity
TS Burcham, DT Osuga, Y Yeh and RE Feeney
The antifreeze glycoproteins (AFGP) of polar fish have the ability to
depress the freezing temperature of water approximately 500 times the
amount expected based on the number of AFGP molecules in solution; yet AFGP
solutions have a purely colligative melting point depression. The
difference of solution melting and freezing temperatures is the antifreeze
activity of AFGP. One characteristic of AFGP activity that requires further
examination is the effect of concentration on antifreeze activity,
especially whether the activity saturates at high concentrations or the
measured activity increases ad infinitum. This study first surveys the
activity of the various antifreeze components from both Pagothenia
borchgrevinki and the Arg-containing antifreeze glycoprotein from Eleginus
gracilis (EgAF). It was found that all AFGP components examined have a
plateau in activity at high concentration, but the actual value of the
plateau activity differs between the different length AFGP components and
between AFGP and EgAF. While the low molecular weight components of both
AFGP and EgAF lose activity at deep supercooling, at high concentration
activity is restored. The activity data is then shown to fit a reversible
kinetic model of AFGP activity, and the coefficients obtained are used to
compare the activity differences between AFGP components and between AFGP
and EgAF. The model is also shown to describe the activity of the
antifreeze protein of the fish Pseudopleuronectes americanus and the
thermal hysteresis protein of the insect, Tenebrio molitor.