Oxidation-reduction potentials of D-amino acid oxidase.

Abstract This paper reports a study of the oxidation-reduction equilibrium of d-amino acid oxidase, a flavoprotein containing FAD. The oxidation-reduction potential at 50% oxidation (E½) is -0.004 volt at pH 7.0 and 20°, and therefore about 180 mv higher than that of the free coenzyme (FAD). This difference in oxidation-reduction potential may be described in terms of relative affinity of the apoenzyme for the reduced and oxidized forms of the coenzyme. On this basis the affinity constant for the binding of reduced FAD to the apoenzyme is about 106 higher than that of oxidized FAD. The curve relating E½ to pH is in the alkaline range consistent with a slope of about -0.058 volt per pH unit which corresponds to the difference of 1 proton between the oxidized and reduced forms of the enzyme. The apparent pK of the oxidation-linke group, which belongs to the oxidized form, is ∼7.1. The shape of the oxidation-reduction equilibrium curve of d-amino acid oxidase is pH dependent, the value of n increasing from about 1 at pH 8.6 to about 3, or more, at pH 6.6. Under these conditions, therefore, one must consider the existence of functional homotropic interactions between at least 2 FAD molecules. The pH dependence of the cooperative oxidation-reduction equilibrium is discussed in the framework of the theory of linked functions

The role of cardiac imaging before and after left atrial appendage standalone thoracoscopic exclusion

Aims: To assess the characteristics of left atrial appendage (LAA) stump and left atrial (LA) volume after standalone totally thoracoscopic LAA exclusion in 40 patients with nonvalvular atrial fibrillation (NVAF) and contraindications to oral anticoagulation (OAC), using cardiac computed tomography (CCT) and transoesophageal echocardiography (TOE). Methods: Using CCT and TOE, we evaluated correct AtriClip Pro II positioning, the presence and characteristics of the LAA stump and the postprocedural LA volume, at 3 months' follow-up. Stump depth was measured with both CCT and TOE using a new method, based on left circumflex artery (LCX) course. Results: After placement of AtriClip, all 40 patients discontinued OAC, and no stroke occurred. LAA exclusion was achieved in 40/40 patients at 3 months' follow-up. LAA stump (depth <10 mm in 12/18 stump, 67%) was observed in 18 patients. The overall (LA + LAA) volume and isolated LA volume were statistically different when comparing cases with and without LAA stump (P < 0.02). LAA ostium dimensions (perimeter and area) and LAA volume correlate with stump depth (P < 0.02). There was a high correlation between CCT and TOE in stump identification and depth measurement (P < 0.02). Compared with the baseline, CCT LA volume increased (P < 0.01) at 3 months' follow-up. Conclusion: Preprocedural and postprocedural CCT and TOE are useful and comparable in patients undergoing standalone totally thoracoscopic exclusion of LAA, because these imaging methods can identify anatomical LAA and LA characteristics predisposing for a postprocedural residual stump