DOWN-REGULATION OF S-ADENOSYL-L-METHIONINE DECARBOXYLASE ACTIVITY OF TRYPANOSOMA-BRUCEI DURING TRANSITION FROM LONG SLENDER TO SHORT STUMPY-LIKE FORMS IN AXENIC CULTURE

Long slender trypanosomes, isolated from infected moose blood or from cryopreserved stabilates, respectively, were unable to grow in conditi oned media (cMEM), prepared from the declining phase of axenic bloodst ream form cultures. Additionally, mixtures of fresh medium and cMEM le d to decreased growth rates and, in accordance to the amount of cMEM u sed, to a decreased S-adenosyl-L-methionine decarboxylase (Ado-MetDC; E.C. 4.1.1.50) activity. Since addition of polyamines could not overco me the process of transition from dividing to non-dividing cells and t he intracellular S-adenosyl-L-methionine (AdoMet), ornithine and putre scine concentrations seemed unaltered during the course of cultivation , we questioned if polyamine metabolism is involved in this transition process. Activities of two key enzymes of polyamine metabolism, AdoMe tDC and ornithine decarboxylase (ODC; E.C. 4.1.1.17) were therefore mo nitored during different growth stages. Our results revealed a specifi c activity of 44 pmol min(-1) mg protein(-1) for AdoMetDC and a K-M of 10 phr for AdoMet. Methylglyoxal bis(guanylhydrazone) showed a K-i of 6 mu M. The constant activity of the enzyme during a 7 h time-course in the presence of cycloheximide indicates a t(1/2) of more than 7 h f or the trypanosomal enzyme. Enzyme activity in trypanosomes isolated f rom infected laboratory animals and from logarithmic phase bloodstream or procyclic form cultures was high according to a high dividing rate , whereas enzyme activity in parasites isolated from the stationary ph ase of bloodstream form culture was negligible. In these cultures, Ado MetDC activity decreased with a t(1/2) of 7 h during transition hom lo ng slender to short stumpy-like forms as soon as the stationary phase was reached. ODC activity was high (approximately 300 pmol min(-1) mg protein(-1)) in dividing trypanosomes isolated from infected animals a s well as from logarithmic phase bloodstream or procyclic form culture s and decreased also during transition with a t(1/2) of 10 h.