Polypeptides, Polyamides, and Proteins

Proceeding to more complex compounds, let us consider the synthetic polymers. A fairly large number have been synthesized, and some of the amides are in commercial production in very large quantities. The most important examples of synthetic polyamides have a medium length carbon chain between the amide groups and differ in structure from the polypeptides. As a result, they are model compounds for proteins only in the /3 or stretched form (see Section 10.4.3 on structural models). 

Although polypeptides were studied as early as 1934 (1393) the real impetus has come since Woodward and Schramm rediscovered the Leuchs polymerization reaction (2194). The English workers were most nimble in following this lead, and several groups attacked the structure problem through the polypeptides (see 76, 292, 36, 123). Bamford, Elliott, and Hanby, in their book (122, pp. 53-58), give a list of synthetic polypeptides and some of their properties. 

In an over-all consideration, the following relatively few facts are well established. In general, polypeptides, like proteins, exist in two forms which Astbury termed a and ]8. Materials with the a form can be stretched by about 100 percent and have an x-ray pattern dominated by polar reflections at 5.1-5.3 A and 1.5 A, and a diffuse equatorial 

The fibrous proteins from hair, quills, silk, feathers, etc., generally exist in one of these forms (a or jS), and all have the same general properties. As might be expected, they show more variation, less crystallinity, and on the whole are more difficult to study, than the synthetic materials. 

Criteria 1, 2, 3, and 6 of Table 10-IV as well as the use of levo configuration and parameters from simple compounds are now well substantiated. Criterion 5, as initially stated, probably went too far, though as yet there is not direct proof of the presence or lack of straight H bonds. The requirement may have to be restated in terms of the angles around the N and O atoms. Criterion 7 will then be decided also. Criterion 8 has a firm basis in Mizushima s work (see references 20 and 21 in our 883) but has not yet been fully demonstrated in actual proteins. 

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