| Abstract: | Studies are reported on the primary structure of human retinol-binding protein (RBP), the specific plasma transport protein for vitamin A. The protein consists of a single polypeptide chain of 186-187 amino acids. RBP was cleaved by cyanogen bromide into five fragments, CB-I (27 residues), CB-11 (25 residues), CB-III (20 residues), CB-IV (15 residues), and CB-V (99-100 residues). The cyanogen bromide fragments were isolated, their compositions were determined, and they were aligned after studies that included the tryptic digestion of maleylated, reduced, and carboxymethylated RBP and subsequent enzymatic digestion of some of the resulting tryptic peptides. The amino acid sequences of four of the five cyanogen bromide fragments were determined, and the sequence of almost two-thirds of the NH2-terminal portion of the RBP molecule was determined as: H2N-GLU-Arg-Asp-Cys-Arg-Val-Ser-ser-Phe-Arg-Val-Lys-Glu-Asn-Phe-Asp-Lys-Ala-Arg-Phe-Ser-Gly-Thr-Trp-Tyr-Ala-Met-Ala-Lys-Lys-Asp-Pro-Glu-Gly-Leu-Phe-Leu-Gln-Asp-Asx-Ile-Val-Ala-Glu-Phe-Ser-Val-Asx-Glx-Gly-Thr-Met-Ser-Ala-Thr-Ala-Gly-Lys-Arg-Val-Arg-Leu-Leu-Asn-Asn-Trp-Asp-Val-Cys-Ala-Asp-Met-Val-Gly-thr-Phe-Thr-Asp-Thr-Glu-Asp-Pro-Ala-Lys-Phe-Lys-Met-Lys-Tyr-Trp-Gly-Val-Ala-Ser-Phe-Leu-Gln-Lys-Gyl-Asn-Asp-Asx-His-Trp-Ile-Val-Asp-Thr-Asx-Thr-Tyr-Tyr-Ala-Val-Glu-Tyr-Cys-Ser-Arg---. |
