Pancreatic enzymes biosynthesis

The first part of this review will be devoted to enzyme biosynthesis by pancreas and the second part to chemical characterization of certain pancreatic enzymes. Some of these enzymes have already been comprehensively discussed in recent volumes of this series (6, 7). 

Tryptophan was first isolated from casein hydrolysates, prepared by hydrolysis using pancreatic enzymes, by Hopkins in 1902. It occurs in animal proteins in relatively low amounts (1-2%) and in even lower amounts in cereal proteins (about 1%). Tryptophan is exceptionally abundant in lysozyme (7.8%). It is completely destroyed during acidic hydrolysis of protein. Biologically, tryptophan is an important essential amino acid, primarily as a precursor in the biosynthesis of nicotinic acid. 

Keller and Cohen (36) also subjected to chromatography acidic extracts of cattle pancreatic microsomes and ribosomes. In microsomes they found the expected amounts of all enzymes which are known to be stable in acid, viz., chymotrypsinogen A, trypsinogen, deoxyribonuclease, and ribonuclease. The amounts of chymotrypsinogen B were abnormally low and ribonuclease B was perhaps not present. The results concerning ribosomes were made somewhat uncertain by the ability of these particles to incorporate proteins from the medium. Nevertheless, a series of characteristic enzymes could be isolated from what appears to be the very site of their biosynthesis. 

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