VAP1 Antibody (Rat mAb) [G15D13]

VAP-1, also designated semicarbazide-sensitive amine oxidase and encoded by the AOC3 gene, belongs to the copper-containing amine oxidase enzyme family and functions as a dual-purpose endothelial molecule, combining catalytic amine oxidase activity with a distinct role as an inducible leukocyte adhesion receptor. The enzyme catalyzes oxidative deamination of primary amines, including the endogenous substrates methylamine and aminoacetone, converting them to the corresponding aldehyde while releasing hydrogen peroxide and ammonia as reaction byproducts; catalysis depends on a copper ion together with a protein-derived topaquinone cofactor, distinguishing VAP-1 structurally and mechanistically from the flavin-dependent mitochondrial monoamine oxidases MAO-A and MAO-B despite the overlapping enzyme classification. Steady-state kinetic analysis using the model substrate benzylamine reveals a bell-shaped pH-dependence of the turnover rate, defined by two macroscopic ionizable groups within the enzyme-substrate complex, indicating that catalysis requires a specific protonation state maintained by residues positioned at the active site during amine turnover. VAP-1 exists in both a membrane-bound form on the surface of vascular endothelial and smooth muscle cells and a soluble circulating form generated through metalloproteinase-mediated proteolytic shedding of the membrane-anchored protein, and expression of membrane-bound VAP-1 is upregulated specifically at sites of vascular inflammation. Functioning as an adhesion molecule, VAP-1 mediates the slow-rolling and firm adhesion steps of the leukocyte adhesion cascade at high endothelial venules and inflamed blood vessels, supporting binding of lymphocytes, monocytes, and granulocytes to the endothelial surface as a prelude to transmigration into tissue, a role mechanistically distinct from its enzymatic amine-oxidizing function even though both activities reside on the same protein. In vascular smooth muscle cells, VAP-1 enzymatic activity toward aminoacetone and methylamine generates cytotoxic aldehyde products and contributes to oxidative stress within the vessel wall, extending VAP-1's pathological relevance beyond leukocyte recruitment into direct vascular tissue damage during atherosclerosis. VAP-1 is implicated in the chronic inflammatory component of atherosclerotic cardiovascular disease, including stroke and coronary artery disease, through its combined contribution to immune cell infiltration of the vessel wall and oxidative modification of vascular tissue, and genetic deletion of AOC3 in mice reduces leukocyte infiltration into adipose tissue, directly linking VAP-1 activity to tissue-specific immune cell recruitment in a model of metabolic and vascular inflammation.

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