Chemistry and Biology of Proteins - F. Haurowitz 1953

Hydrolytic Cleavage of Proteins
Amino Acid Sequence in the Peptide Chain

Quantitative data on the Amino Acid Composition of Proteins, presented in Table 1, are essential for characterizing a protein and elucidating its Structure. However, these data do not yet reveal the arrangement of Amino Acids within extended peptide chains or the distribution of various amino acids within the protein globule. It is readily apparent that the physical and Chemical properties of two proteins containing identical Amino acids can differ significantly if the molecular surface of one protein is formed by dissociating amino acids, whereas that of the other is formed by non-polar amino acids. Consequently, it is impossible to predict the PHYSICOCHEMICAL PROPERTIES OF a given protein solely on The basis of its amino acid percentages.

Until relatively recently, nothing was known about The sequence of amino acids in protein peptide chains. Valuable insights in this regard have been gained only over the past few years through the fractionation of partial Protein Hydrolysis products. Sanger [53] investigated Peptides isolated from the degradation of Insulin (see Chapter XIII). The terminal amino groups of these peptides were labeled by Condensation with dinitrofluorobenzene (see Chapter VII). It was found that upon further hydrolysis, the isolated peptides yielded DNP-glycylisoleucine (where DNP symbolizes dinitrophenyl), DNP-glycylisoleucylvaline, and DNP-glycylisoleucylvalylglycine. On this basis, it was concluded that the amino acids in these peptides are arranged in the following order: Glycine—isoleucine—valine—glycine. Other DNP-peptides were isolated from the enzymatic hydrolysate of DNP-insulin [126]. Similarly, it was found that the partial hydrolysis of the bacterial toxin gramicidin S yields the following dipeptides and tripeptides: valylornithine, ornithylleucine, leucylphenylalanine, phenylalanylproline, prolylvalylornithine, valylornithylleucine, and phenylalanylprolylvaline. From this, it was concluded that gramicidin S contains an amino acid chain that closes to form a cyclopeptide: L-valine-L-Ornithine-L-leucine-D-phenylalanine-L-Proline¹ [127] (see Chapter XV). The Separation of peptide mixtures in these studies was performed using paper Chromatography [29] or countercurrent distribution [126].

Although these studies provided information regarding The structure of only small segments of peptide chains, their significance is exceptionally high, as they bring us directly to The problem of constructing the backbone of the protein molecule from its hydrolytic degradation products.

¹ According to recent data, gramicidin S is not a pentacyclopeptide, but a decacyclopeptide (A. R. Battersby, L. C. Craig, J. Am. Chem. Soc., 73, 1887, 1951). — Ed. note.