Amino acid sequence, of insulin

The procedure described in Sections 27.8-27.11 was used to determine the amino acid sequence of insulin. 

Using procedures such as those outlined in this section more than 100 proteins have been sequenced. This is an impressive accomplishment considering the complexity and size of many of these molecules (see, for example, Table 25-3). It has been little more than two decades since the first amino acid sequence of a protein was reported by F. Sanger, who determined the primary structure of insulin (1953). This work remains a landmark in the history of chemistry because it established for the first time that proteins have definite primary structures in the same way that other organic molecules do. Up until that time, the concept of definite primary structures for proteins was openly questioned. Sanger developed the method of analysis for N-terminal amino acids using 2,4-dinitrofluorobenzene and received a Nobel Prize in 1958 for his success in determining the amino-acid sequence of insulin. 

For almost a decade there was a continuing dispute over the exact nature of insulin s chemical composition until it was finally accepted that the hormone was in fact a protein. Sanger established the amino acid sequence of insulin in 1960, and this led to the complete synthesis of the protein in 1963, and to the elucidation of its three-dimensional structure in 1972. Insulin was the first hormone for which a radioimmunoassay was developed (1978) and the first to be produced by genetic engineering (given to human volunteers in the summer of 1980). 

Determining the Amino Acid Sequence of Insulin Figure 3-24 shows the amino acid sequence of the hormone insulin. This structure was determined by Frederick Sanger and his coworkers. Most of this work is described in a series of articles published in the Biochemical Journal from 1945 to 1955. 

The studies of Sanger and co-workers (1945-1955) on the amino acid sequence of insulin provide the best example of the use of partial acid hydrolysis for determination of the covalent structure of polypeptides. When oxidized A- or B-chains were submitted to hydrolysis in 11-12 iV HCl... 

Shuffle test. An enzyme that catalyzes disulfide-sulfhydryl exchange reactions, called protein disulfide isomerase (PDl), has been isolated. PDI rapidly converts inactive scrambled ribonuclease into enzymatically active ribonuclease. In contrast, insulin is rapidly inactivated by PDI. What does this important observation imply about the relation between the amino acid sequence of insulin and its three-dimensional structure ... 

Frederick Sanger in 1953 determined the complete amino acid sequence of insulin for the first time. The important steps involved in determining the primary structure of protein are -... 

The amino acid sequence of insulins from various animal species has been examined. Details of these are shown in Table 25-6. Il is apparent from the antilysis that frequent changes in sequence occur within the inlerehain di.sulfide ring (positions 8, 9, and 10). The hormonal. sequence fur porcine insulin is the closest lo lhal of humans, differing... 

In 19S3, Frederick Sanger determined the amino acid sequence of insulin, a protein hormone (Figure 2.22). This work is a landmark in biochemistry because it showed for the first time that a protein has a precisely defined amino acid sequence consisting only of L amino acids linked by peptide bonds. This accomplishment stimulated other scientists to carry out sequence studies of a wide variety of proteins. Currently, the complete amino acid sequences of more than 2,000,000 proteins are known. The striking fact is that each protein has a unique, precisely defined amino acid sequence. The amino acid sequence of a protein is referred to as its primary structure. 

RIO. Rinderknecht, E., and Humbel, R. E., The amino acid sequence of insulin-like growth factor I and its structural homology with proinsulin. /. Biol. Chem. 253, 2769-2776 (1978). 

The amino acid sequence of insulin does not determine its three-dimensional structure. By catalyzing a disulfide-sulfhydryl exchange, this enzyme speeds up the activation of scrambled ribonuclease because the native form is the most thermodynamically stable. In contrast, the structure of active insulin is not the most thermodynamically stable form. The three-dimensional structure of insulin is determined by the folding of preproinsulin, which is later processed to mature insulin. 

The glycine residue at position 8 in the amino acid sequence of insulin has torsion angles of ( ) = 82° and / = -105° that lie in the unfavorable region (marked X) of the Ramachandran plot in Fig. 4-9. How is this possible ... 

Table I. Amino Acid Sequences of Insulins from Various Species Aligned with the Amino Sequences of IGF and Relaxin... 

FIGURE 15.10 The amino acid sequence of insulin, which contains 51 amino acids in two chains linked by disulfide bonds (Section 15.9) between the side chains of cysteine residues. 

Frederick Sanger discovers the amino acid sequence of insulin. 

Among others, they are of historical importance, particularly insulin. The decade of work by Sanger and co-workers on the amino acid sequence of insulin represents pioneering research into the primary structure of a protein. 

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