Cytochrome b561 can be detected in many neuroendocrine tissues using a specific monoclonal antibody.

CG7 is a monoclonal antibody that recognizes cytochrome b561, a major protein component of adrenal medullary chromaffin granules. Immunocytochemical studies using this antibody have demonstrated that cytochrome b561 is present in many neural and endocrine tissues and that its distribution is correlated with the presence of either catecholamines or amidated peptides in the tissue. These tissues include neuronal cell bodies and/or fibers in the gut, blood vessels, retina, and posterior pituitary, endocrine cells of the gut, anterior and intermediate lobes of the pituitary, heart muscle, and all adrenal medullary chromaffin cells. The discovery of cytochrome b561 in many neuropeptide-containing tissues regardless of the presence of catecholamines is consistent with a general role for cytochrome b561 as a secretory granule membrane electron carrier. Its expression may be linked to an ascorbic acid requirement by both catecholamine and neuropeptide biosynthetic enzymes.