Abstract
The complete amino acid sequence of phospholipase A2 (PLA2) from the pyloric ceca of the starfish Asterina pectinifera was determined by automated Edman degradation. The A. pectinifera PLA2 (APLA2) consists of 137 amino acids with an unblocked N-terminus and its molecular weight is calculated to be 15 300.1. The enzyme contains 14 cysteine (Cys) residues at the corresponding positions of the same residues which have been shown to be involved in intramolecular disulfide bonds in mammalian pancreatic PLA2. The region involving an active site and a Ca2+-binding loop shows fairly high sequence homology (75%) between the APLA2 and porcine pancreatic PLA2. The APLA2 conserved the amino acid sequence of the loop portion of the porcine pancreatic PLA2 except for the deletion of two amino acids. These features indicate that the APLA2 can be classified into the group 1 type PLA2. In contrast, the homology between the APLA2 and porcine pancreatic PLA2 was calculated to be 47% in the whole region. Further, the insertion of sixteen residues and the deletion of three residues were required in the sequence of the APLA2 to align the corresponding region to the β-wing of porcine pancreatic PLA2. These differences in amino acid sequence of the APLA2 may account for its specific properties such as the higher activity and the characteristic substrate specificity.
