Binding of diamine oxidase activity to rat and guinea pig microvascular endothelial cells. Comparisons with lipoprotein lipase binding.

Abstract

Microvascular endothelial cells from rat and guinea pig fat pads were shown to bind diamine oxidase (DAO) activity when incubated with soluble extracts of placenta (33 DAO U/mg of placenta) and a purified placental enzyme preparation (94 U/ gg of protein). The extent of binding was dependent on the concentration of enzyme activity and tissue. Saturation of binding sites with 5,000 U of DAO/ml resulted in levels of bound activity (up to 11-13 U/mg of endothelial cells) in excess of that observed in all tissues except placenta. Scatchard plots suggested that there were at least two DAO binding sites (apparent K., 92 and 2,450 U/ml). Although the same cell preparations bound 125I-labeled lipoprotein lipase (LPL), the presence of LPL on the endothelial cell surface did not interfere with the binding of DAO activity except when cells were exposed to high concentrations of LPL. Alternatively, bound DAO activity was partially displaced (up to 33%) only with high concentrations (30 zg/ml) of LPL. DAO activity may thus be bound to at least two populations of sites, one of which may bind LPL. Both enzymes, however, were displaced by heparin (0.05-5 U/ml) and DAO binding was impaired by prior treatment of cells with proteolytic and glycosaminoglycandegrading enzymes. The demonstration of DAO binding to vascular endothelial cells provides a further example of the ability of these cells to bind enzymes at their surface and thereby act on biologically active substances in the circulation.

Plasma clearance of human extracellular-superoxide dismutase C in rabbits.

“…Given the large pores in the sinusoids, hepatocytes are also possible sites in the liver. For several other plasma factors with heparinn affinity (like lipoprotein lipase, hepatic lipase, and platelet factor 4) that are rapidly released by intravenous heparin, there are indications that the endothelial cell surface receptor is the heparin analogue heparan sulfate (18,19). It is probable that heparan sulfate is also the receptor for EC-SOD C. Heparan sulfate is found on the surface ofmost cell types in the body (20).…”

On the binding of tumor necrosis factor (TNF) to heparin and the release in vivo of the TNF-binding protein I by heparin.

“…Lipoprotein lipase and diamine oxidase are both rapidly released into the circulation by heparin (20,21). These substances can bind to endothelial cells, a binding which is sensitive to glycosaminoglycan degrading enzymes (22).…”

Diamine Oxidase: An Overview of Historical, Biochemical and Functional Aspects

“…About 60% are present in the organ elles and the rest free in the cytosolic compart ment. In the majority of studies it has been hypothesized that after synthesis DAO is translocated to heparin-sensitive binding sites in the capillaries of the lamina propria [55]. This location may prevent polyamine cross ing from the intestine into the circulation.…”