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Absence of any detectable activity of the membrane marker enzyme 5'-nucleotidase in human red blood cells.

We have investigated in human red blood cell membranes the presence of a 5'-nucleotidase, which is considered a general marker of plasma membranes. No activity was detectable with a highly sensitive colorimetric method. This absence is not due to the rapid decline of enzyme activity in the course of red cell ageing, nor to its release during membrane preparation; nor is it due to substrate accessibility hindrance to the active center of the enzyme. Thus, the ubiquitousness of 5'-nucleotidase in plasma membranes is questioned.