Inhibition of SSAO activity by small molecular SSAO inhibitors and by VAP-1Y471F mutation. Uninfected (native), pADENO-lacZ-, pADENO-VAP-1-, and pADENO-VAP-1Y471F-infected HUVECs were treated with the vehicle (-) or with SSAO inhibitors (SC + HA = semicarbazide + hydroxylamine, BTT = BTT-2027 compound) and antibodies (HB116 against HLA class I, TK8-14 against VAP-1), and the enzymatic activity was determined using the radiochemical method. The specific activities (mean ± SEM from 3 independent assays) are shown. The SSAO-dependent H₂O₂ production in HA + SC-treated native HUVECs is 0 by definition. Note that the VAP-1Y471F mutant is devoid of any SSAO activity and that the anti-VAP-1 mAb does not interfere with the SSAO activity.