Do mammalian amine oxidases and the mitochondrial polyamine transporter have similar protein structures?

Polyamine transport across the mitochondria membrane occurs by a specific, common uniporter system and appears controlled by electrostatic interactions as for polyamine oxidative deamination by bovine serum and mitochondrial matrix amine oxidases was found. In fact in all the cases, while the catalytic constants or the maximum uptake rate values show little changes with the number of the positive charges of the substrates, Michaelis–Menten constant values demonstrate exponential dependence, confirming that electrostatic forces control the docking of the substrate into the enzyme active site or polyamine channel. By the treatment of the kinetic data in terms of Gibbs equation or Eyring theory, the contribution of each positive charge of the polyamine to the Gibbs energy values for the oxidative deamination of polyamines by two mammalian amine oxidase and for polyamine transport, are obtained. These values were comparable and in good accordance with those reported in literature. Previous studies demonstrated that two negative functional groups in the active site of bovine serum and mitochondrial matrix amine oxidases interact electrostatically with three positive charges of the polyamines in the formation of the enzyme– substrate complex. Remembering the structure–function relationship of proteins, our results suggest analogous interactions in the polyamine transporter and, as a conse- quence, a partial structural similitude between two proteins. It follows that the primary sequences of the amino oxidases and the mitochondrial transport may, in part, be conserved.