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Regulation of human lympho blast plasma membrane 5' nucleotidase ec 3.1.3.5 by zinc


Journal of Biological Chemistry 257(22): 13544-13549
Regulation of human lympho blast plasma membrane 5' nucleotidase ec 3.1.3.5 by zinc
Human lymphoblasts lose > 90% of their plasma membrane 5'-nucleotidase activity within 24 h when grown in Zn-deficient (< 0.05 .mu.M Zn(II)) culture media prepared with either bovine serum albumin/fatty acids/transferrin or with extensively dialyzed fetal bovine serum as supplements. The loss of 5'-nucleotidase activity is accompanied by a decrease in substrate affinity. The inactivation of plasma membrane 5'-nucleotidase is temperature-dependent and requires the metabolically active cell. When isolated plasma membranes are incubated under the same conditions as the whole cells, they do not lose their 5'-nucleotidase activity. Supplementation of the Zn-deficient culture media with 10 .mu.M Zn prevents the loss of 5'-nucleotidase activity. Addition of 10 .mu.M Zn to Zn-deficient cells or plasma membranes prepared from cells with low 5'-nucleotidase activity due to Zn depletion leads to complete recovery of activity within 24 h. The recovery is not prevented by inhibition of protein synthesis. The reactivation of 5'-nucleotidase shows a dependence on temperature which is clearly distinct from the inactivation process. The addition of Co(II), Cu(II) or Cd(II) to Zn-deficient cultures leads to some activation of 5'-nucleotidase, but none of the divalent cations tested are nearly as effective as Zn. The observed changes in 5'-nucleotidase activity were not found in other divalent cation-requiring plasma membrane enzymes (ATPase, alkaline phosphatase). Apparently, plasma membrane 5'-nucleotidase can exist as an inactive apoenzyme and Zn plays a unique role in the expression of plasma membrane 5'-nucleotidase activity.


Accession: 006288550



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