In animals, the peripheral benzodiazepine receptor is a mitochondrial protein ( located in the outer mitochondrial membrane ) characterised by its ability to bind with nanomolar affinity to a variety of benzodiazepine-like drugs, as well as to dicarboxylic tetrapyrrole intermediates of the haem biosynthetic pathway.
22.
In these two examples, a metal is complexed at the center of a tetrapyrrole macrocycle ring : the metal being iron in the heme group ( iron in a porphyrin ring ) of hemoglobin, or magnesium complexed in a chlorin-type ring in the case of chlorophyll.
