Studies on the Effects of Infusion of Enzyme Inhibitors on Mouse Adenosine Deaminase
Two inhibitors of adenosine deaminase, 9- erythro -(2-hydroxy-3-nonyl)adenine (EHNA) and 9-β-D-arabinofuranosyl-6-hydroxylaminopurine (ara-HA), which represent relatively tight and weak binding substrate analogues, respectively, were infused into mice over a period of 5 days. Nine different tissues...
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Veröffentlicht in: | Molecular pharmacology 1978-01, Vol.14 (1), p.199-209 |
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Zusammenfassung: | Two inhibitors of adenosine deaminase, 9- erythro -(2-hydroxy-3-nonyl)adenine (EHNA)
and 9-β-D-arabinofuranosyl-6-hydroxylaminopurine (ara-HA), which represent relatively tight and weak binding substrate analogues,
respectively, were infused into
mice over a period of 5 days. Nine different tissues were excised, and adenosine
deaminase activity levels, as well as selected kinetic parameters and electrophoretic
variants, were characterized. Isoelectric focusing demonstrated two variants (adenosine
deaminases I and II) that focused in the pH range 4.65-4.75 and exhibited an
approximate apparent molecular weight of 36,000 by gel filtration. The ratio of these
two forms, which differed from tissue to tissue, was unaffected by the inhibitor
infusions. Striking increases in adenosine deaminase activity were observed after the
infusions and were found to vary with the tissue as well as the nature and dose of
inhibitor. Activities in the lung, stomach, liver, and jejunum increased by about 8-, 3-,
3-, and 2-fold, respectively, after infusion of no more than 0.6 mg/ml of EHNA. Other
tissues displayed significant but smaller increases. The effects of ara-HA were generally
smaller than those of EHNA, except in the jejunum, ileum, and thymus. Inhibition of
adenosine deaminase in vitro by EHNA, and to a lesser extent by ara-HA, also varied
from tissue to tissue, but did not correlate with the ratio of adenosine deaminases I and
II. Adenosine deaminase partially purified from mice treated with a higher dose of
EHNA (5.0-7.5 mg/ml) displayed a significantly lower K i value for EHNA; smaller
decreases were noted in the K m , for adenosine. The most striking change was observed
in the K m of adenosine deaminase II for EHNA, which changed from 14.9 nM (control)
to 3.1 nM (after infusion). By classical Ackermann-Potter plots EHNA was shown not
to be a titrating or stoichiometric inhibitor either before or after the infusions. EHNA
in all cases showed classical competition with substrate. The data may be of value in
the development of combined chemotherapy regimens involving adenosine deaminase
inhibitors as well as in understanding the molecular basis of the role of adenosine
deaminase in regulating cell division. |
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ISSN: | 0026-895X 1521-0111 |