Early in an
infection the bloodstream forms of the African trypanosome Trypanosoma brucei brucei are long, slender and rapidly dividing. Later, non-dividing, short, stumpy forms may be found. In this report we described biochemical differences between the two parasite populations in the phosphorylation of their
proteins in vitro. Compared with the slender populations, the non-dividing stumpy forms of the parasites exhibit decreased phosphorylation of an 80 kDa
protein and enhanced phosphorylation of 37 kDa and 42 kDa
proteins (pp37 and pp42). These changes occurred regardless of whether the stumpy trypanosomes were generated naturally during the course of the
infection or induced by
difluoromethylornithine treatment. The phosphorylation of pp37 and pp42 occurs on
serine and
threonine residues and is totally dependent upon the presence of Mn2+ or Mg2+. However, excess Mn2+ or Mg2+ inhibits phosphorylation. Maximal phosphorylation of pp42 occurs with 1 mm-Mn2+ or 10 mm-Mg2+, whereas that of pp37 occurs with 50 mM-Mn2+ or greater than 100 mm-Mg2+. The phosphorylation of pp37 is greatly enhanced by KCl, whereas that of pp42 is only slightly increased by this
salt. Ca2+,
calmodulin,
phospholipids and
cyclic AMP have no discernible effect upon the phosphorylation of pp42 or pp37 in vitro, whereas
heparin,
suramin,
polylysine,
polyarginine and
polyamines all inhibit phosphorylation. Thus the
enzymes that phosphorylate pp42 and pp37 have properties similar to, but distinct from, those of mammalian
casein kinase II. Since the
casein-kinase-like activity is higher in the slender than in the stumpy forms, the enhanced phosphorylation of pp42 and pp37 in the non-dividing parasites is probably a result of the enhanced synthesis of these acidic
proteins.