Cellular retinol-binding protein (type two) is abundant in human small intestine

Human small intestine was found to contain a retinol-binding protein similar to the gut-specific cellular retinol-binding protein, type two [CRBP (II)], described in the rat. This newly detected human protein was immunochemically distinct from human cellular retinol binding protein previously described but immunochemically similar to rat CRBP (II). The partially purified protein bound retinol and exhibited fluorescence excitation and emission spectra distinct from those spectra for retinol bound to pure human CRBP but similar to the spectra for retinol bound to rat CRBP (II). Human CRBP (II) could be localized to the villus-associated enterocytes by immunohistochemistry, using antiserum against rat CRBP (II). The protein was abundant representing 0.4% of the total soluble protein in a jejunum mucosal extract. This protein may play an important role in the absorption and necessary intestinal metabolism of vitamin A.