Amino Acid Composition and NH2-Terminal Amino Acid Sequence of Rat Platelet Secretory Phospholipase A21

Abstract

The amino acid composition and partial NH ² -terminal amino acid sequence of the phospholipase A ² secreted by stimulated rat platelets were determined. The most predominant amino acid in the phospholipase A ² was cysteine followed by lysine, suggesting that it is a basic one. This finding is consistent with its high affinity to a cation exchange column. The NH ² -terminal 24 amino acids were found to be as follows: X-Leu-Leu-Glu-Phe-Gly-Met-IIe-Leu-phe-Lys-Thr-Gly-Lys-Arg-Ala-Asp-Val-Ser-Tyr-Gly-Phe-Tyr-Gly- The enzyme contains ⁵ Phe, ⁸ Met, ⁹ lle, ²⁴ Tyr, and ²⁵ Gly residues, all of which are conserved in the sequenced pancreatic phospholipase A ² .This is the first report of the tentative characterization of a cukaryotic phospholipase A ² , the cellular source of which is known,i.e., it does not originate from a venom or the pancreas.