AMP deaminase, the activity that catalyzes the deamination of
AMP to form
IMP and NH3 has been measured in Dictyostelium discoideum. A new procedure to assay the activity of this
enzyme was developed using
formycin 5'-monophosphate, a fluorescent analog of
AMP as the substrate, and ion-paired reverse phase HPLC to separate the reactants and products. Quantitation of the
formycin containing compounds was accomplished at 290 nm. At this wavelength
adenosine containing compounds were not detected and activity could be monitored in the presence of its activator
ATP. The
AMP deaminase activity in vegetative cells was 7.4 nmols/min/mg
proteins while the activity in cells measured at 2 and 6 hrs after
starvation-induced growth-arrest was 376 nmols/min/mg
protein...a 51-fold increase. When vegetative cells were treated with
hadacidin, a
drug that restricts de novo
AMP synthesis and pinocytosis, the activity of the
AMP deaminase was 511 nmols/min/mg
protein...a 70-fold increase compared to that in untreated vegetative cells. Smaller increases were noted following the inhibition of growth with the drugs
cerulenin and
vinblastine, as well as after the inhibition of de novo GMP synthesis with the
drug mycophenolic acid or the partial inhibition of de novo
AMP synthesis with analogs of
hadacidin, N-hydroxyglycine and
N-formylglycine. In addition, when the activity of two other
enzymes involved in
purine metabolism, namely
adenosine kinase and
hypoxanthine-
guanine phosphoribosyl
transferase, was measured in vegetative cells, and the activity of both compared to that measured in
starvation and
hadacidin induced growth-arrested cells, showed no significant changes.(ABSTRACT TRUNCATED AT 250 WORDS)