It was reported previously that rat platelets release phospholipase A
2 upon
in vitro stimulation by thrombin, ADP, or A23187 (Horigome, K., Hayakawa, M., Inoue, K., & Nojima, S. (1987)
J. Biochem. 101, 53-61). Secretion of phospholipase A
2 was also observed with rabbit platelets. Rabbit platelets seem to release phospholipase A
2 upon stimulation
in vivo, because the rabbit plasma taken immediately after intravenous injection of PAF contained an appreciable level of phospholipase A
2 activity and fewer platelets. Rabbit platelet phospholipase A
2 released
in vitro was purified by column chromatography using Sepharose CL-4B conjugated with anti-rat platelet derived phospholipase A
2 monoclonal antibody, followed by reversed-phase HPLC. The purified enzyme was subjected to structural analysis by HPLC peptide mapping and primary sequence determination of the separated peptides. Based on the homology with rat platelet secretory phospholipase A
2 (Hayakawa, M., Kudo, I., Tomita, M., Nojima, S., & Inoue, K. (1988)
J. Biochem. 104, 767-772), a partial primary structure (62 amino acid residues) of the rabbit enzyme was tentatively determined; the two sequences were highly homologous (72%). The rabbit sequence was also nearly identical to that of rabbit ascitic fluid phospholipase A
2, which was determined by Forst
et al. (Forst, S., Weiss, J., Elsbach, P., Maraganore, J. M., Reardon, I., & Heinrikson, R. L. (1986)
Biochemistry 25, 8381-8385). Phospholipase A
2 from the membrane fraction of rabbit platelets was also purified; it had the same characteristics and the same amino-terminal sequence as the purified secretory enzyme. Secretory and membrane-bound phospholipase A
2 of rabbit platelets may in fact be identical.
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