gamma-Glutamyltransferase: normal cortical levels in Alzheimer disease.

gamma-Glutamyltransferase (EC 2.3.2.2; gamma-GT) may be important in the transport of amino acids or peptides across the blood-brain barrier. Gamma-GT activities were the same in cortical samples from Alzheimer and age-matched control brains, and there was no correlation between gamma-GT and choline acetyltransferase (ChAT) or acetylcholinesterase (AChE) levels, both of which were significantly reduced in the Alzheimer samples. ChAT and AChE activities were significantly correlated in both groups. ChAT showed a negative correlation with age in the controls and a positive correlation in the Alzheimer group. The opposite was true for gamma-GT, although the correlations were of low significance. The results do not lend any support to the hypothesis of a defect in the blood-brain barrier in Alzheimer disease.