Introduction

The importance of proteins, substances responsible for primary functions in the living cell, need not be stressed any more. We may pay tribute to the nomenclator who from the Greek protos (first) or proteios (primary) coined the word protein. This foresight or intuition, usually attributed to Jac. Berzelius, remains vindicated in spite of the most impressive progress in nucleic acid chemistry and the emergence of DNA as the carrier of genetic information and RNA as template in protein biosynthesis. Nucleic acids provide the blueprint for the construction of complex machinery, the machines themselves are proteins. In fact, information encoded in DNA-s and in RNA-s is operative only in the presence of enzymes, that is proteins. It is clear therefore, that protein chemistry is one of the most important chapters of biochemistry, and can even stand by itself as the subject of a textbook. It is perhaps less obvious why peptide chemistry should be treated separately. The term “peptide” (from pepsis = digestion or peptones = digestion products of proteins) denotes relatively small compounds which are quite similar to proteins except that the latter are substances of higher molecular weight. The reasons for this distinction are not self evident. There is no distinct borderline between the two groups of materials; molecules built of 100 or more amino acid residues are usually regarded as proteins and those containing a lesser number of residues as peptides.