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Levels of adenosine deaminase, AMP deaminase, and adenylate kinase in cultured human lymphoblast lines: Exquisite sensitivity of AMP deaminase to adenosine deaminase inhibitors

Biochemical Medicine, ISSN: 0006-2944, Vol: 26, Issue: 3, Page: 377-386
1981
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A dozen human cell lines have been compared with peripheral blood lymphocytes for specific activity levels of three enzymes. Adenylate kinase was normal in all lymphoblast cultures, but was severalfold higher in the one erythromyeloid cell line studied. Adenosine deaminase was normal in all B-cell lines, and was markedly elevated in all T-cell lines. AMP deaminase levels were notably low in 9 of the 12 cell lines. Most striking were the results of inhibition trials with three adenosine deaminase inhibitors: coformycin, 2′-deoxycoformycin, and EHNA. The adenosine deaminase of cultured blast cells and mature peripheral blood cells was about equally sensitive to these inhibitors with I 50 values about 45, 20, and 200 n m, respectively. The AMP deaminase of all cultured blast lines tested was 10–100 times more sensitive to the coformycins than was their adenosine deaminase, and 1–10 times as sensitive to EHNA. In contrast, the AMP deaminase of peripheral blood lymphocytes and erythrocytes was 1000 times less sensitive than their adenosine deaminase, and behaved like the AMP deaminase purified from human muscle. In the K562 erythromyeloid cell line, which can be induced to differentiate, a biphasic inhibition pattern was obtained, with the two inhibitor constants separated by four orders of magnitute, suggesting the presence of both blast-cell-type and mature-cell-type isozymes. The transition from inhibitor-sensitive to -insensitive AMP deaminase may there-fore be involved in, or provide a marker for, cell differentiation. If lymphoblasts in vivo are similarly constituted, then treatment with these inhibitors will evoke effects due to blockade of AMP deaminase as well as adenosine deaminase. Certainly their use in lymphoblast cultures to prevent degradation of labeled adenosine may vitiate conclusions on the role of AMP deaminase in purine nucleotide metabolism.

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