Phospholipase leaves

Figure 4. Effect of pH on total phospholipase activity in A. culture filtrates of fungus grown on rye steep media + 10 mg PC for 7 days. B. Culture wash of fungus grown on lima bean agar for 14 days. C. Potato leaf, uninfected or infected for 7 days. D. Infected potato leaf (7 days) assayed in the presence of 5 mM dithioreitol (DTT-insensitive activity). DDT-sensitive activity was calculated by subtracting the phospholipase activity in the presence of DDT from that measured in the absence of DDT. Reproduced with permission from Ref. 4. Copyright 1984, Academic Press.

Kates (1955) extended the research of earlier workers on the degradation of PC by plant extracts. The action of phospholipase D was readily measured by the release of choline, but the release of water-soluble organic phosphate and inorganic phosphate was also measured. Spinach leaf extracts were particularly effective in releasing inorganic phosphate. A 15,(XK)-g particulate fraction of leaf homogenate was used for the assay. The pH optimum for phosphate release was 5 it was pointed out that this may reflect the pH optimum for the release of PA, that is, the action of phospholipase D. 

Dyer, J.H., Ryu, S.B. and Wang, X. (1994) Multiple forms of phospholipase D following germination and during leaf developmnet of Castor bean. Plant. Physiol. 105, 715 - 724. 

Davidson, F. M., and C. Long The structure of the naturally occurring phosphoglycerides. 4. Action of cabbage-leaf phospholipase D on ovolecithin and related substances. Biochem. J. 69, 458—66 (1958). 

The only other plant enzyme which has been reported to be stimulated by the same three treatments is isofloridoside-phosphate synthase (4) as previously described. Those authors presented evidence for the presence of an endogenous acid protease which could stimulate the enzyme. They also proposed (4) that calmodulin and protein kinase somehow stimulated this protease which in turn proteolytically-activated the isofloridoside-phosphate synthase. Such a mechanism is also conceivable for the potato leaf phospholipase. The only other plant enzyme which has been reported to be stimulated by proteolytic activation is a glucan synthase in soybean cells (6). It is also interesting to note that an animal phospholipase, pancreatic phospholipase A, is activated by the proteolytic removal of a heptapeptide from the ammo terminus (7). 

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