Eminent chemists of our time . alies or suchenzymes as pepsin and trypsin, which are found in thestomach and pancreas respectively. The changes thatthe protein undergoes in the stomach and the smallintestine can be duplicated in the laboratory, and it isthen shown that this hydrolysis proceeds in stages, givingus metaproteins, primary proteoses, secondary proteoses,peptones, polypeptids and amino acids—all more orless well-defined substances, whose chemical complexityis greatest at the protein end, and simplest at the amino-acid end. The crude physical methods of classifying proteinshave point
Eminent chemists of our time . alies or suchenzymes as pepsin and trypsin, which are found in thestomach and pancreas respectively. The changes thatthe protein undergoes in the stomach and the smallintestine can be duplicated in the laboratory, and it isthen shown that this hydrolysis proceeds in stages, givingus metaproteins, primary proteoses, secondary proteoses,peptones, polypeptids and amino acids—all more orless well-defined substances, whose chemical complexityis greatest at the protein end, and simplest at the amino-acid end. The crude physical methods of classifying proteinshave pointed to the fact that there are some 40 to 50 innumber. All of these, when hydrolysed, give a largepercentage of the 19 amino-acids which are common tomost proteins; the differences among proteins is mostmarked in the amount of the various amino-acids whichthey yield when hydrolysed. Due in no small part to the labors of Fischer and hisco-workers, most of these nineteen amino-acids havebeen synthesised from simpler bodies. 230. EMIL FISCHER If the hydrolysis of proteins, and the investigation ofthe decomposition products so produced was a difficulttask, what are we to say of the reverse process, whereby,by starting with ammo-acids, we build up proteins?* Yet that is what Fischer did. He succeeded in work-ing out methods by which amino-acids could be chemi-cally joined on to one another in some such way as thelinks of a chain. He has given the name poly pep tidsto such combinations of amino-acids. In his most celebrated experiment in the synthesis ofproteins, Fischer succeeded in combining eighteenamino-acids—an octadecapeptid—which is one of themost complicated artificial substances that has everbeen produced, and which shows some very strikingresemblances to the natural proteins, not the least ofwhich is the way trypsin, the pancreatic enzyme, breaksit up into the amino-acids out of which the artificialprotein was built. The enzymes, as the reader may remember, arespecific
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