FURTHER CHARACTERIZATION OF THE LIPOPROTEIN ICE NUCLEATOR FROM FREEZE TOLERANT LARVAE OF THE CRANE-FLY TIPULA-TRIVITTATA

1. Using Western blots, immunological similarities were found between the hemolymph lipoprotein ice nucleator (LPIN) from freeze tolerant larvae of the cranefly Tipula trivittata and the ice nucleator protein from the bacteria Pseudomonas fluorescens, indicating the presence of some amount of the well known repeat structure of the bacterial protein in the LPIN. 2. Delipidated LPIN apoproteins are inactive, but activity can be regained by reconstitution of the two apoprotein components of the LPIN with phosphatidylinositol (PI) in proteoliposomes. Substitution of PI-4,5-diphosphate or PI-4-monophosphate for PI in reconstitutions resulted in greatly reduced activity. 3. Treatment of the LPIN with periodate eliminated activity. 4. Thus, the presence of both apoproteins plus the integrity of the hydroxyls of the inositol head group of PI seem to be essential for ice nucleator activity of the LPIN.