Kinetic aspects of human platelet monoamine oxidase thermolability

Monoamine oxidase in platelets collected on two different occasions, from twelve apparently healthy subjects, were studied. The influence of human platelet poor plasma (PPP) on MAO thermolability and variation in enzyme activity over time was investigated. A 30–70% reduction of the activity was observed after heat treatment at 52°C for 30 min. Activity of MAO was determined before (C) and after heat treatment (H). No significant differences between the H/C ratios on the two occasions were observed for either Vo, Vmax or Km with or without 10% PPP added to the incubates. A temporal increase of the kinetic parameters was observed. The magnitude of this increase was smaller for vo than for apparent Km and Vmax. Platelet MAO activity regulation by human PPP is discussed.