Involved in oxygen transport from the lung to the various peripheral tissues. Hemopressin acts as an antagonist peptide of the cannabinoid receptor CNR1. Hemopressin-binding efficiently blocks cannabinoid receptor CNR1 and subsequent signaling. Heterotetramer of two alpha chains and two beta chains. Red blood cells. This alpha chain has an extra residue (Gln-116) in the region between the G and H helices. Belongs to the globin family.