Carboxylate groups heme locations

Regarding the chemical modification of the heme molecule located in the active site of peroxidases and other heme-proteins with peroxidase activity, a few examples are now discussed. Free carboxylic groups of heme from horse heart cytochrome c... 

A number of other cytochromes are located in the intermembrane space and the inner surface of the outer mitochondrial membrane. Cyt bs (cytochrome b ) is a small heme protein with a hydrophihc domain of about 95 amino acids and a carboxyl terminus of about 45 hydrophobic amino acids that serve to anchor the protein to the inner surface of the outer mitochondrial membrane. Cyt bs is reduced by NADH-cyt bs reductase, also located on the inner surface of the outer membrane. Under conditions of high intermembrane ionic strength, Cc is released from the inner membrane, and can transport electrons from cyt bs on the outer membrane to CcO on the inner membrane. Cyt bs contains protoheme b with the iron atom hgated by two histidine nitrogen atoms. The heme group has a reduction potential of -1-10 mV versus NHE. Cyt bs is also found on the liver endoplasmic reticulum membrane, where it transfers electrons from NADH-cyt b ... 

It is a major surprise (98) to find a bis(Met)heme with such a low redox potential (Table II) and a possible explanation for this is that the heme is located in a region of the protein with a relatively high local negative charge density arising from carboxylic acid groups. 

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