L-asparaginase of Tetrahymena pyriformis is associated with a kinase activity |
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Authors: | Stella-Anna E Tsirka Dimitrios A Kyriakidis |
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Institution: | (1) Laboratory of Biochemistry, Faculty of Chemistry, School of Science, Aristotelian University of Thessaloniki, 54006 Thessaloniki, Greece;(2) Laboratory of Biochemistry, Faculty of Chemistry, Aristotelian University of Thessaloniki, Thessaloniki, Greece |
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Abstract: | 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 -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. |
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Keywords: | L-asparaginase protein kinase Tetrahymena pyriformis |
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