Inhibitory effect of C-reactive protein on phospholipase D activity

C-reactive protein (CRP) was found to inhibit the phospholipase D activity significantly with dose dependency. Addition of 15 micrograms/ml CRP resulted in about 60% decrease in phospholipase D activity using phosphatidylcholine dispersed with Triton X-100 as substrate, and more using lipid suspension consisting of only phosphatidylcholine. In Lineweaver- Burk analysis with phosphatidylcholine dispersed with Triton X-100, the apparent Km value of phospholipase D for phosphatidylcholine increased from 2.27 mg/ml to 3.72 mg/ml by addition of 7.5 micrograms/ml CRP whereas the Vmax value was not altered. The possible usefulness of CRP as phospholipase D inhibitor was discussed.