The stereoselective recognition of substrates by phosphoinositide kinases.

Soluble phosphatidylinositol (PtdIns) 4- and 3-kinase activities were partially purified and characterized from human placental extracts. The placental PtdIns 4-kinase (type 3) has a K(m) for ATP of 460 M and is kinetically different to a partially purified human erythrocyte, membrane- bound, PtdIns 4-kinase (type 2). These three inositol lipid kinases were then used to compare their substrate specificities against the four synthetic stereoisomers of dipalmitoyl PtdIns. Only the placental 4-kinase was influenced by the chirality of the glycerol moiety of PtdIns. However, neither of the 4-kinases was able to phosphorylate. L-PtdIns and, therefore, these kinases have an absolute requirement for the inositol ring to be linked to the glyceryl backbone of the lipid through the D-1 position. Phosphoinositide 3-kinase, on the other hand, was found to phosphorylate both D- and L-PtdIns. While the 3-kinase phosphorylated exclusively the D-3 position of D-PtdIns, further analyses demonstrated that the same enzyme phosphorylated two sites on L-PtdIns, namely the D-6 and D-5 positions of the inositol ring. Some implications of these findings are discussed

Lipoprotein-associated phospholipase A(2) as an independent predictor of coronary heart disease

Background: Chronic inflammation is believed to increase the risk of coronary events by making atherosclerotic plaques in coronary vessels prone to rupture. We examined blood constituents potentially affected by inflammation as predictors of risk in men with hypercholesterolemia who were enrolled in the West of Scotland Coronary Prevention Study, a trial that evaluated the value of pravastatin in the prevention of coronary events. Methods: A total of 580 men who had had a coronary event (nonfatal myocardial infarction, death from coronary heart disease, or a revascularization procedure) were each matched for age and smoking status with 2 control subjects (total, 1160) from the same cohort who had not had a coronary event. Lipoprotein-associated phospholipase A(2), C-reactive protein, and fibrinogen levels and the white-cell count were measured at base line, along with other traditional risk factors. The association of these variables with the risk of coronary events was tested in regression models and by dividing the range of values according to quintiles. Results: Levels of C-reactive protein, the white-cell count, and fibrinogen levels were strong predictors of the risk of coronary events; the risk in the highest quintile of the study cohort for each variable was approximately twice that in the lowest quintile. However, the association of these variables with risk was markedly attenuated when age, systolic blood pressure, and lipoprotein levels were included in multivariate models. Levels of lipoprotein-associated phospholipase A(2) (platelet-activating factor acetylhydrolase), the expression of which is regulated by mediators of inflammation, had a strong, positive association with risk that was not confounded by other factors. It was associated with almost a doubling of the risk in the highest quintile as compared with the lowest quintile. Conclusions: Inflammatory markers are predictors of the risk of coronary events, but their predictive ability is attenuated by associations with other coronary risk factors. Elevated levels of lipoprotein-associated phospholipase A(2) appear to be a strong risk factor for coronary heart disease, a finding that has implications for atherogenesis and the assessment of risk