Nature's Robots: A History of Proteins

By Charles Tanford; Jaqueline Reynolds | Go to book overview

CHAPTER 3
The peptide bond

The type of condensation described here through formation of
–CO–NH–CH= groups may thus explain both the building up of
protein substances in the organism, as well as their breakdown in the
intestinal tract
and in the tissues. On the basis of these given facts one
may therefore consider the proteins as for the most part arising by
condensation of α-amino acids, whereby the linkage through the
group –CO–NH–CH= has to be regarded as the regularly recurring
one.

Franz Hofmeister, 19021


Introduction: proteins are built up from amino acids

By 1900 it was understood that protein molecules are mainly built up from amino acids and most of the constituent amino acids had been identified—a huge change in the frame of reference compared to 1840, the year of Mulder’s elemental analyses, when only glycine and leucine had been known. The rest had gradually appeared over the years, isolated from protein hydrolysates and chemically characterized. Emil Fischer, one of the two principal figures in this chapter, himself added two to the list, namely proline and valine, first isolated in his laboratory in 1901. One could not know at the time what the ultimate total would be, but in fact only three remained to be discovered—five if we count asparagine and glutamine. Actual dates are given in Table 3.1.

Retrospectively, asparagine and glutamine merit special mention. We now realize the similarity between their amide bonds and the peptide bonds of proteins: asparagine and glutamine would normally have been hydrolysed to the corresponding acids in the course of protein breakdown. This hydrolysis was actually anticipated as early as 1873 by Hlasiwetz and Habermann, on the basis of the knowledge that ammonia is always a product of complete protein decomposition.6 They considered it very likely that the ammonia was originally derived from

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