Bursicon: Its effect on tyrosine permeation into insect haemocytes

Abstract

When haemolymph of Pieris brassicae is incubated in isotonic solutions, tyrosine, a normal constituent of insect haemolymph, is rapidly metabolized with concomitant deterioration of the system. This reaction may be prevented by adding 10 −4 M sodium diethyldithiocarbamate to the incubates. In these stabilized haemocyte suspensions as a rule no tyrosine conversion occurs. If bursicon, the cuticle-hardening hormone, is added to such stabilized cell suspensions tyrosine conversion starts immediately, and proceeds at a rate depending on the amount of bursicon added. Ca 2+ and Mg 2+ accelerate this reaction. Since the enzyme system converting tyrosine into DOPA, and the latter to dopamine, has been shown to reside within the haemocytes, whereas the substrate tyrosine occurs in the serum, the above results are considered as evidence in proof of the hypothesis of Mills, R.R. and Whitehead, D.L. (1970) J. Insect Physiol. 16, 331–343, that the function of bursicon is to render the haemocyte membrane permeable to tyrosine.