We purified pancreatic deoxyribonuclease I (DNase I) from the shark Heterodontus japonicususing three-step column chromatography. Although its enzymatic properties resem-bled those of other vertebrateDNases I, sharkDNase I was unique encoding theDNases I of two shark species,H. japonicusandTriakis scyllia, were constructed from their total pancreatic RNAs using RACE. Nucleotide sequence analyses revealed two structural alterations unique to shark enzymes: substitution of twoCys residues at positions 101 and 104 (which are well conserved in all other vertebrate DNases I) and insertion of an additional Thr or Asn residue into an essential Ca 2+ -binding site. .
