A Cytosolic Phospholipase A2 from Potato Tissues Appears to Be Patatin

Phospholipase (PL) A₂ is involved in signal transduction inthe resistance reaction that is induced in potato by inoculationof an incompatible race of Phytophthora infestans, the lateblight fungus, or by treatment with fungal elicitor hyphal wallcomponents (Kawakita et al. 1993). In this study, PLA₂ in thesoluble fraction from potato tuber was purified. The followingresults suggested that the enzyme was, in fact, patatin: (1)the molecular mass of the purified enzyme was 40 kDa, the sameas that of patatin; (2) the pI of the purified enzyme was approximately4.75, which corresponds to that of patatin; and (3) the amino-terminalamino acid sequence of the purified enzyme showed a high degreeof homology to that of patatin. Patatin is known as a storageprotein of the potato tuber and it has been shown to have esteraseactivity. However, other enzymatic activities and the function(s)of patatin are unknown. We investigated the PLA activities ofthe purified patatin. The PLA₂ activity of the patatin was muchhigher than the PLA₁ activity, even though the protein exhibitedboth activities. The PLA₂ activity of the enzyme was particularlyapparent when phosphatidylcholine with linoleic acid at thesn-2 position was used as substrate. Lower activity was observedwith phosphatidylcholine with palmitic acid, oleic acid andarachidonic acid at the sn-2 position. (Received October 5, 1995; Accepted February 9, 1996)