Ribonuclease activities and distribution in Alzheimer's and control brains.

Levels of free and total alkaline ribonuclease, and levels of acidic ribonuclease, were measured postmortem in control brains and in the brains of patients with Alzheimer's disease. In each brain region assayed, whether control or Alzheimer's, there was a statistically significant difference between the levels of free and total alkaline ribonuclease. Between 59 and 90% of the enzyme activity was associated with alkaline ribonuclease inhibitor in an inactive complex. Levels of free and total alkaline ribonuclease varied widely among different brains and brain regions, and were always lower in cerebellum than in temporal cortex and occipital pole. There was no significant difference in the levels of total alkaline ribonuclease, free alkaline ribonuclease, or acidic ribonucleases between corresponding regions of Alzheimer's and control brains. There was also no qualitative difference in the subcellular distribution of the alkaline and acidic ribonucleases between Alzheimer's and control brain. No significant relationships were found between ribonuclease levels and age, neuritic plaque density, postmortem interval, or storage time.