Pools of polymerized and total tubulin were measured in human platelets as a function
of free sulfhydryl groups both in acid-soluble and acid-precipitable cell fractions.
Changes in free thiols were produced either by storage of platelets at room temperature
or by addition of the potent oxidizing agent diazene dicarboxylic acid (diamide) and
were correlated with shifts in the dynamic equilibrium between assembled and disassembled
microtubules and platelet aggregation. Diamide at concentrations of 0.5 to 5 mM depleted
acid soluble SH groups and reduced protein thiols while causing a progressive decrease
in polymerized tubulin. Similar changes, although not as severe, were initiated by
storage of platelets at room temperature. Platelet aggregation especially that induced
by collagen showed a positive correlation with the pool of polymerized tubulin. Our
results indicate that the state of oxidation of sulfhydryl groups especially in the
acid- precipitable fraction plays an important role in determining the position of
equilibrium between polymerized and depolymerized tubulin.
Keywords
Microtubule protein - Platelets - Sulfhydryl groups - Polymerized and depolymerized
tubulin
