Peptidase increase accompanying growth of the larval salivary gland of Drosophila melanogaster.

1. The larval salivary gland of Drosophila melanogaster offers an opportunity to study growth in a tissue in which no cell division occurs but in which the cells increase in size. 2. Measurements of alanylglycine (AG)-peptidase content have been made in three stocks of Drosophila melanogaster at different growth stages of the larval salivary gland, and have been correlated with its total nitrogen and volume. 3. During the prepupal instar, the AG-peptidase content of the gland increases parallel with total nitrogen but decreases when histolysis of the gland begins. Conversely, a benzoyl-l-arginineamide-hydrolyzing endopeptidase is not measurable until histolysis sets in. 4. In the final larval growth period of a giant mutant, there is a concomitant increase in peptidase, total nitrogen, and volume of the gland. 5. A similar association of peptidase content and total nitrogen is found in comparing glands of different sizes from the giant stock, at the time of maximal peptidase content in the prepupa. 6. The data are interpreted as evidence for an association of AG-peptidase with growth of the cells in the gland. This agrees with the earlier interpretation by Linderstrøm-Lang and Holter of data obtained from study of more complex tissues. 7. A survey of the available measurements of peptidase content in other organisms shows that wherever an increase of cell substance occurs, peptidase content increases. Conversely, peptidase remains constant where cell division is unaccompanied by an increase of cell substances. 8. The joint association of peptidases and pentosenucleic acids with protein synthesis is pointed out. 9. The possiblity is considered that peptidases may be essential parts of a unit in which coupled reactions necessary for protein synthesis occur. The rôle of the peptidases in this system is discussed. They may act either synthetically to form new peptide linkages (problematic), or hydrolytically to mobilize the necessary specific amino acids.