By means of heparin-affinity and glycyrrhizin (GL)-affinity column chromatographies (HPLC), a GL-binding phospholipase A
2 (gbPLA
2) was selectively purified from the synovial fluids of patients with rheumatoid arthritis. This purified gbPLA
2 was identified as a secretory type IIA PLA
2 (sPLA
2-IIA) since it was crossreacted with anti-sPLA
2-IIA serum. The activity of purified sPLA
2-IIA was inhibited by glycyrrhetinic acid (GA) and a GA derivative (oGA) in a dose-dependent manner, but it was more sensitive to GA than GL. Furthermore, it was found that (i) purified sPLA
2-IIA is phosphorylated by casein kinase II (CK-II) in vitro; (ii) this phosphorylation induces in a significant stimulation of PLA
2 activity; and (iii) oGA at one-tenth the concentration of GL inhibits the CK-II-mediated stimulation of sPLA
2-IIA activity. These results show that (i) sPLA
2-IIA is a GL-binding protein; and (ii) CK-II mediates stimulation of its PLA
2 activity in vitro.
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