The family of EF-hand type Ca2+-binding proteins includes calbindin (previously designated vitamin D-dependent Ca2+-binding protein), S-100 alpha and beta, calgranulins A (also designated MRP8), B (also designated MRP14) and C (S-100 like proteins) and the parvalbumin family members, including parvalbumin alpha and parvalbumin B, also designated oncomodulin (OCM). Structurally and evolutionarily conserved, parvalbumin alpha and OCM proteins are distinct in expression and function. Parvalbumin alpha, also designated parvalbumin (PV), is most abundantly expressed in fast-contracting muscles with lower expression levels in brain and some endocrine tissues, including kidney and parathyroid. Research indicates that parvalbumin alpha plays a significant role in muscle relaxation. OCM was originally thought to have expression restricted to neoplastic tissues, early embryonic cells and certain tumor cell lines. Recent research shows that OCM is also expressed and secreted by macrophages where, in the retina it binds to retinal ganglion cells (RGCs) and functions to promote axon regeneration. OCM has also been detected in the auditory sensory cells of the organ of Corti in mammals. In humans, two different loci on chromosome 7 have been identified as OCM and OCM-like (LOC4951). These genes encode proteins 109aa in length which share 99% sequence identity.