An Improved Procedure for Automated Edman Degradation Used for Determination of the N-Terminal Amino Acid Sequence of Human Transcobalamin I and Human Intrinsic Factor

Abstract

An improved procedure for automated Edman degradation is presented. Three programs are described, one with double cleavage and two with single cleavage. The programs presented are characterized by a reversed delivery scheme for buffer and phenyl isothiocyanate, and by reduced cleavage times. The modified procedures applied on automated Edman degradation of the vitamin B12-binding proteins human transcobalamin I and human intrinsic factor, containing approximately 390 and 350 amino residues respectively, gave the following N-terminal amino acid sequences: Human transcobalamin I Glu-Ile-Cys-Glu-Val-Ser-Glu-Glu-Asn-Tyr-Ile-Arg-Leu-Lys-Pro-Leu-Leu-Asn-Thr-Met-Ile-Gln-Ser-Asn-Tyr-Asn-?-Gly- Human intrinsic factor Ser-Thr-Gln-Thr-Gln-Ser-Ser-Cys-Ser-Val-Pro-Ser-Ala-Gln-Glu-Pro-Leu-Val-Asn-Gly-Ile-Gln-?-Leu-Met-Glu-Thr- The background accumulation seems to be related not only to the length of the polypeptide chain being degraded, but also to the content of serine (and possibly threonine). A possible N leads to O acyl shift during the cleavage is a tentative explanation. The programs here represented lead to a significant reduction in background compared to conventional programs and allowed considerable prolongation of the degradations.