HORMONAL CONTROL OF TURNOVER OF TYROSINE AND TYROSINE PHOSPHATE DURING TANNING OF ADULT CUTICLE IN FLY SARCOPHAGA BULLATA

The only soluble metabolite of 14C-tyrosine injected into flies as they emerge from their puparia is tyrosine-O-phosphate. A kinetic study of its turnover in the presence and absence of the adult tanning hormone, bursicon, indicates that it is probably not an intermediate in the tanning process. Its rôle may be that of a store of metabolically accessible tyrosine. However, since the specific activity of tyrosine falls during the first 5 hr of adult life after emergence and there is insufficient tyrosine phosphate to account for the observed dilution rates, it is suggested that a proteinaceous or peptide precursor is degraded at this time. The parallel dilution rate of 14C lysine lends support to this possiblity. © 1969.