Major outer membrane proteins matrix protein

The above describes the major pathway of proteins destined for the mitochondrial matrix. However, certain proteins insert into the outer mitochoiidrial membrane facilitated by the TOM complex. Others stop in the intermembrane space, and some insert into the inner membrane. Yet others proceed into the matrix and then return to the inner membrane or intermembrane space. A number of proteins contain two signaling sequences—one to enter the mitochondrial matrix and the other to mediate subsequent relocation (eg, into the inner membrane). Certain mitochondrial proteins do not contain presequences (eg, cytochrome Cy which locates in the inter membrane space), and others contain internal presequences. Overall, proteins employ a variety of mechanisms and routes to attain their final destinations in mitochondria. 

Kameyama et al. [10] have applied SEC/LALLS technique to study porin, a major matrix protein of Escherichia coli outer membrane. The protein retains an oligometric structure in presence of SDS and dissociates to monomers on heat treatment [29]. The molecular weight of oligomer and monomer can thus be measured in the same buffer containing SDS. 

PPi is made in three ways (1) in the nucleus as a by-product of RNA synthesis (nNTP —> NMPn + nPPi) (2) in the cytosol as a by-product of amino acid activation for protein synthesis (aa + ATP —> aaAMP + PPi) and (3) by acetyl CoA synthetase on the outer mitochondrial membrane prior to its degradation for ATP production (R-COOH + ATP + HS-CoA —> R-Co-SCoA + AMP + PPi). Amino acid activation is the major source of cytosolic PPi, which is transported by the ANK protein to the osteoid matrix to inhibit premature mineralization (see Sect. 9.3.5). 

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