Master of Science
Richard R. Mills
The presence of an adenyl cyclase system within the haemocyte of Periplaneta americana has been confirmed by previous investigations, with corresponding experiments using dibutyryl cyclic AMP to show enhancement of 14c-tyrosine uptake into the cuticle linked to stimulation of the sclerotization process.
In the present studies, American cockroaches held at depressed temperatures were treated with bursicon, revealing an increase in haemocyte cyclic AMP concentrations. The levels declined with progression of time, probably resulting from enzymatic hydrolysis.
When animals which had been held at room temperature were treated with bursicon, the levels of haemocyte cyclic AMP were lowered, with a declination to sub-control levels with time progression. These results were' duplicated using dihydroxyphenylethylamine (dopamine) and isobutylmethylxanthine in the treatment medium.
Analysis of haemocyte protein binding by cyclic AMP revealed large amounts bound by proteins greater than sixty.thousand daltons. Any remaining cyclic AMP was either unbound or converted to one of several metabolites. Inhibition of phosphodiesterase by removal of a sulfhydryl protecting agent and addition of EDTA caused a net decrease in protein bound label and an increase in intact cyclic AMP recovered from the reaction. Bursicon added to the reaction caused a slight depression of the binding reaction, presumably due to competition by native cyclic AMP.
The addition of dibutyryl cyclic AMP to haemocyte preparations resulted in net increases in uptake of tyrosine and leucine into the cells as a function of the dibutyryl cyclic AMP concentration. The levels of uptake were enhanced corresponding to each concentration level of dibutyryl cyclic AMP, but did not maintain their rapid uptake rates over an extended time course.
Results presented in this work indicated that the mode of action of bursicon is via adenyl cyclase activation and resultant cyclic AMP production. Rapid binding reactions to enzymes such as phosphodiesterase and protein kinase appear to regulate the actions of cyclic AMP in the haemocyte.
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