Summary
Normal human platelets have been separated according to density on continuous Percoll
gradients and the platelet distribution divided into five fractions containing approximately
equal numbers of platelets. The mean volumes and protein contents of the platelets
in each fraction were found to correlate positively with density while the protein
concentration did not differ significantly between the fractions. Four mitochondrial
enzymes (monoamine oxidase, glutamate dehydrogenase, cytochrome oxidase and NADP-dependent
isocitrate dehydrogenase) were assayed and their activities per unit volume were found
to increase in a very similar monotonie fashion with platelet density. When MAO and
GDH were assayed on the same set of density fractions the correlation between the
two activities was very high (r = 0.94–1.00, p <0.001) and a similar close correlation
was found between MAO and ICDH. The results support the hypothesis that high density
platelets either have a higher concentration of mitochondria or have larger mitochondria
than low density platelets.
Key words
Platelet density - Platelet monoamine oxidase - Platelet mitochondria - Platelet NADP-dependent
isocitrate dehydrogenase