We have established in vitro conditions under which we can reliably measure
kinase activity in normal postmortem human brain. Using these conditions, we detected in the brains of patients with
Alzheimer disease a 2-fold increase in the level of Mr 60,000
protein phosphorylation compared to age-matched controls. The Mr 60,000
protein phosphorylation was found exclusively in the cytosol fraction. No differences were detected between
phosphoproteins in 100,000 X g pellet fractions from brains of
Alzheimer disease patients and from age-matched controls. Postmortem time up to 17 hr does not seem to affect the phosphorylation level of the Mr 60,000
protein. Younger
Alzheimer disease patients had more prominent changes in the elevation of the Mr 60,000
protein phosphorylation level than older patients, although in the control patient, age did not affect the phosphorylation level of the Mr 60,000
protein. We conclude that in the brain cytosol of
Alzheimer disease there may be an abnormality in either the degree of Mr 60,000
protein phosphorylation or in the Mr 60,000
protein concentration.