Studies on the structure and activity of low molecular weight glycoproteins from an antarctic fish

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.

Variations in macromolecular antifreeze levels in larvae of the darkling beetle, Meracantha contracta

Overwintering larvae of the darkling beetle, Meracantha contracta, produce a macromolecular antifreeze that is similar in activity to the glycoproteinaceous and proteinaceous antifreezes found in some cold-water, marine teleost fishes. The antifreeze is not present in the hemolymph of the Meracantha larvae in summer, but its production begins by late September in the wild population. The antifreeze reaches a maximum concentration in February, decreases slowly through spring, and disappears by early June. The supercooling points of the larvae are lowest in February, when the antifreeze levels are highest, and increase as the antifreeze concentrations in the hemolymph decrease in the spring. Larvae collected in mid-February and warm-acclimated lost the antifreeze with-in 12 days. Larvae collected in early September and cold-acclimated required nearly two months to produce concentrations of antifreeze comparable to those of overwintering larvae. Temperature seems to be the major environmental factor responsible for the control of antifreeze levels in Meracantha; however, other environmental factors may also be involved.

Aglomerularism in Antarctic fish

Urine formation in antarctic bony fish does not involve glomerular filtration. Evidence for aglomerularism came from both direct observation of kidney serial sections by light microscopy and the low concentrations of inulin labeled with carbon-14 that were excreted into the urine when this renal clearance tracer was injected into the bloodstream via a cannula implanted in the caudal vein. Aglomerularism most likely prevents urinary loss of glycoproteins with biological antifreeze properties.