Summary
The “GP I fraction” seen on polyacrylamide gel electrophoresis of reduced samples
of whole normal platelets contains three glycopolypeptides corresponding to the integral
membrane protein GP I (GP Ia), the easily solubilized membrane protein GPS (GP Ib,
glycocalicin) and a granule-located glycoprotein.
Freezing and thawing of platelets in tris-buffered saline leads to a lysis of platelets
and platelet granules with the result that both GPS and the granule glycoprotein is
found in the soluble fraction. The two glycoproteins can be separated by SDS polyacrylamide
gel electrophoresis both in reduced and unreduced samples when urea and EDTA is incorporated
into the gels. This permitted electrophoretic studies of GPS using the granule glycoprotein
as a control and marker substance.
A working hypothesis stating that the presence of GPS on the platelet surface is a
prerequisite to the agglutination of human platelets with bovine factor VIII related
protein, has been investigated. The hypothesis was supported by the observation that
storage of platelets in tris-buffered saline at 4° C led to the elution of GPS and
loss of agglutination, as was also the case when platelets were frozen and thawed
in tris-buffered saline, or preincubated in 3 M KCl and resuspended in either tris-buffered
saline or the EDTA-containing medium A. GPS was not, or only slightly, solubilized
when platelets were frozen and thawed in the EDTA-containing medium and the resulting
platelet ghosts still agglutinated.
Platelets from 1 patient of the Bernard-Soulier type did not agglutinate with the
bovine factor VIII-related protein, nor did the platelets contain GPS. An improved
technique for the isolation of such platelets is described.
