The effect of an amino acid analog on catheptic activity in somite mesoderm of the chick embryo

1. 1. In the somite mesoderm of 45-hour chick embryos (Hamburger and Hamilton's stage 11) there is a higher catheptic activity in the unsegmented region than in the region that has already undergone segmentation. 2. 2. The somite mesoderm of embryos cultured for 10 hours on an agar-glucose medium containing 0.15 mg/ml of the leucine analog W-bromoallylglycine (BAG) has a markedly higher catheptic activity than somite mesoderm of control embryos cultured without BAG. 3. 3. These results confirm the indications from Schultz and Herrmann's study (1958)of the rate of uptake of radioactive glycine into these tissues, which were that there is an abnormally high rate of protein breakdown in BAG-treated somite mesoderm. 4. 4. The findings are compared with those of von Hahn and Lehmann (1958) using a leucine analog on Xenopus larvae. The role of cathepsins in embryonic development, and the significance of individual amino acids for particular steps in differentiation, are discussed.