Volume 1

The chemical constitution of the proteins / by R.H.A. Plimmer.

  • Plimmer, Robert Henry Aders, 1877-1955.
Date:
1912-1913
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The chemical constitution of the proteins / by R.H.A. Plimmer. Source: Wellcome Collection.

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    hydrolysis is finished. Further hydrolysis is required if the biuret test is positive. Many proteins are hydrolysed with great slowness, as has been pointed out by Osborne and Jones who, by making use of Van Slyke’s method for estimating amino groups, find that hydrolysis with concentrated hydrochloric may only be complete after two to five days. The length of time of hydrolysis is therefore of primary importance * for a complete analysis. Hugounenq, who has employed hydrofluoric acid, finds that the results depend on the strength of the acid; the stronger the acid the greater is the amount of complex polypeptides. Many hours’ boiling with dilute acid are required to effect complete hydrolysis. Abderhalden, Medigreceanu and Pincussohn have compared the hydrolysis by acids and alkalies. Alkali seems to produce the most complete hydrolysis. Abderhalden and Brahm found that a resistant body formed from silk could only be completely hydrolysed by alkali. The main difference in the results of hydrolysis by acids and alkalies consists in the products; the optically active amino acids are com- pletely racemised by the alkali, whereas acids only produce partial racemisation. Arginine is destroyed by boiling with alkali and con- verted into ornithine and ammonia. Cystine is also decomposed by alkali. The Isolation and Estimation of the Units. The amino acids which compose* the protein molecule can be divided into two main groups:— A. The monoamino acids, including proline and oxyproline. Tyrosine and cystine are usually treated independently. B. The diamino acids, including histidine. The three compounds in this group were formerly called the hexone bases on account of their basic properties and the fact that each of them contains six carbon atoms. The remaining unit, tryptophane, is almost completely destroyed by hydrolysis by acids; it can only be isolated after hydrolysis by trypsin. Ammonia is estimated by hydrolysing the protein with concentrated hydrochloric acid, removing the great excess of acid by evaporation under reduced pressure, adding excess of magnesia, distilling off the ammonia in vacuo and collecting it in excess of standard acid. This operation is usually carried out in the determination of the distribution of the total nitrogen amongst the two main groups. The