L-asparaginase of Tetrahymena pyriformis is associated with a kinase activity.
Most of L-asparaginase activity of Tetrahymena pyriformis was found to be present in microsomal membranes from which it has been purified to homogeneity (Tsirka, S.A.E. and Kyriakidis, D.A. Mol. Cell. Biochem. 83: 147-155, 1988). The native enzyme has a relative molecular weight of approximately 200 kDa, while under denaturing conditions the enzyme exhibits a subunit size of 39 kDa. Aminoacid analysis and an oligopeptide from N-terminal sequence have been determined. Dephosphorylation of L-asparaginase by alkaline phosphatase results in an activation of its catalytic activity. This enzyme also exhibits intrinsic phosphorylation activity with a Km value for ATP of 0.5 mM. Autophosphorylation with [gamma-32P] ATP of purified L-asparaginase results in the phosphorylation of tyrosine residues as well as in loss of its activity. Mg2+ and Ca2+ added together act synergistically to stimulate the kinase activity by more than 160%. The polyamines putrescine, spermidine and spermine activate the kinase approximately 100%, while neither cAMP or cGMP have any effect. These results indicate that this membrane protein with dual L-asparaginase/kinase activity must play an important role in regulating the intracellular levels of L-asparagine in Tetrahymena pyriformis.
Tsirka
S A
SA
Faculty of Chemistry, School of Science, Aristotelian University of Thessaloniki, Greece.
Kyriakidis
D A
DA
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001215:Asparaginase / Q000032:analysis / Q000378:metabolism*; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D013379:Substrate Specificity; D013696:Temperature; D013769:Tetrahymena pyriformis / Q000201:enzymology*; D014443:Tyrosine / Q000378:metabolism
D000596:Amino Acids; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D001215:Asparaginase