THE AMINO-ACID-SEQUENCE OF IGUANA (IGUANA-IGUANA) PANCREATIC RIBONUCLEASE

The pyrimidine-specific ribonuclease superfamily constitutes a group o f homologous proteins so far found only in higher vertebrates. Four se parate families are found in mammals, which have resulted from gene du plications in mammalian ancestors. To learn more about the evolutionar y history of this superfamily, the primary structure and other charact eristics of the pancreatic enzyme from iguana (Iguana iguana), a herbi vorous lizard species belonging to the reptiles, have been determined. The polypeptide chain consists of 119 amino acid residues. The positi ons of insertions and deletions in the sequence are identical to those in the enzyme from snapping turtle. However, the two enzymes differ a t 54% of the amino acid positions. Iguana ribonuclease contains no car bohydrate, although the enzyme possesses three recognition sites for c arbohydrate attachment, and has a high number of acidic residues in a localized part of the sequence.