THE EFFECT OF FIXATION WITH FORMALDEHYDE AND GLUTARALDEHYDE ON THE COMPOSITION OF PHOSPHOLIPIDS EXTRACTABLE FROM RAT HYPOTHALAMUS

Fixation of rat hypothalamus in 4% formaldehyde + 1% CaCl 2 for 24 hr at 0°C reduced the amount of extractable ethanolamine phospholipids considerably. This decrease may be caused by hydrolytic cleavage of the vinyl ether bond in phosphatidalethanolamine and by reaction of formaldehyde with the free amino groups in ethanolamine phospholipids. Evidence is presented that the reaction with free amino groups may be the main cause for the decrease of extractable phospholipids when dealing with a fixative that contains glutaraldehyde and is buffered at pH 7. In this case no phosphatidylserine and hardly any phosphatidylethanolamine could be detected in the tissue extract. It is presumed that these phospholipids are fixed to proteins by the cross-linking action of glutaraldehyde involving free amino groups of proteins and phospholipids.