Ca2D Binding and Transport: A Novel Function for Coenzyme Q

Coenzyme Q10 (CoQ10) is one of the essential components of the mitochondrial electron-transport chain (ETC) with a primary function to transfer electrons along and protons across the inner mitochondrial membrane (IMM). The concomitant proton gradient across the IMM is essential for the process of oxidative phosphorylation and consequently ATP production. We report that CoQ10 and its analog CoQ1 have an as-of-yet unknown potential in Ca2þ binding and transport. Using voltammetry, UV-VIS spectrometry, electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) we show that the native form of both CoQ10 and its analog CoQ1 neither bind nor transport Ca2þ ions. However, when exposed to alkaline media or monoxygenase enzymes such as cytochrome P450, both CoQs undergo structural changes through a complex reaction pathway and form quinone structures with distinct properties. In a time dependent manner, one or both methoxy groups at position 2 and 3 on the quinone ring are replaced by a hydroxyl group. Contrary to the native form, the new hydroxylated products (of CoQ1 or CoQ10), depending on its redox transformation, are effectively chelating and transporting Ca2þ across artificial biomimetic membranes. Our results open new perspectives about the physiological importance of CoQ10, not only as electron and proton transporter, but also as a potential regulator of mitochondrial Ca2þ homeostasis