**2. Mitochondrial outer membrane transport proteins**

The mitochondrial outer membrane (MOM) is characterized by higher lipid content than inner membrane and is permeable to small molecules such as sucrose, salts, adenine nucleotides, coenzyme A, and tRNA. It is not permeable to larger molecules such as inulin, polyglucose, cytochrome c, or albumin [1]. The outer mitochondrial membrane contains three integral membrane protein families. The entire translocation and insertion of nearly all newly synthesized proteins destined to the mitochondrial organelle is mediated through channels as part of larger protein complexes, translocase of the outer membrane (TOM complex), the sorting and assembly machinery (SAM) complex (followed by translocase of the inner membrane of mitochondria (TIM)) [2]. Channels, generally, are used to conduct ions and cycle between open and closed states, with some also exhibiting an inactivation step forming a completely continuous tunnel through a bilayer that allows for rapid conductance of many ions [3]. The third protein family are voltagedependent anion channels (VDAC), which are permanently open under physiological conditions with some evidence-based regulations [4]. VDAC is the most abundant protein of outer mitochondrial membrane (∼ 10 thousand copies per mitochondrion), whose functions in permeability of compounds between cytosol and mitochondria have been shown to be related either to physiological or pathological states [5–7]. Many cases of abnormal manifestations of mitochondria are the consequence of this type of regulation of the mitochondrial outer membrane permeability [8].
