Primate Monocytes - CD14, CD16 - Ziegler-Heitbrock

The C2-like b-barrel domain mediates the Ca²⁺-dependent resistance of 5-lipoxygenase activity against inhibition by glutathione peroxidase-1

Abstract

Recently, we reported that in crude enzyme preparations, a monocyte-derived soluble protein (M-DSP) renders 5-lipoxygenase (5-LO) activity Ca2+-dependent. Here we provide evidence that this M-DSP is glutathione peroxidase (GPx)-1. Thus, the inhibitory effect of the M-DSP on 5-LO could be overcome by the GPx-1 inhibitor mercaptosuccinate and by the broad spectrum GPx inhibitor iodoacetate, as well as by addition of 13(S)-hydroperoxy-9Z,11E-octadecadienoic acid (13(S)-HPODE). Also, the chromatographic characteristics and the estimated molecular mass (80-100 kDa) of the M-DSP fit to GPx-1 (Mw = 87 kDa), and GPx-1, isolated from bovine erythrocytes, mimicked the effects of the M-DSP. Intriguingly, only a trace amount of thiol (10 M GSH) was required for reduction of 5-LO activity by GPx-1 or the M-DSP. Moreover, the requirement of Ca2+ allowing 5-LO product synthesis in various leukocytes correlated with the respective GPx-1 activities. Mutation of the Ca2+-binding-sites within the C2-like domain of 5-LO resulted in strong reduction of 5-LO activity by M-DSP and GPx-1, also in presence of Ca2+. In summary, our data suggest that interaction of Ca2+ at the C2-like domain of 5-LO protects the enzyme against the effect of GPx-1. Apparently, in presence of Ca2+, a low lipid hydroperoxide level is sufficient for 5-LO activation.