Abnormal properties of creatine kinase in Alzheimer's disease brain: Correlation of reduced enzyme activity and active site photolabeling with aberrant cytosol-membrane partitioning

The report shows that Alzheimer's disease (AD) brain creatine kinase (CK) is modified such that the nucleotide binding site of CK is blocked and that abnormal partitioning of CK between the soluble and pellet fractions occurs. First, CK activity was 86% decreased in AD brain homogenates in comparison to age-matched controls. Secondly, over a 23.5 fold greater P-32 photoincorporation of [alpha(32)P]8N(3)ATP was observed into CK of control vs. AD samples. Also, a 7.4-fold increase of enzyme induced P incorporation was observed in controls vs. AD samples by incubation with [gamma(32)P]ATP. Thirdly, Western blot analysis showed that CK copy numbers in the AD homogenate were decreased by less than 14% in comparison to controls. However, analysis showed that control supernatant and pellet fractions contained 10.3 and 0.4 times the CK copy number found in the corresponding AD fractions. P-32 incorporation by both photolabeling and enzyme catalyzed incorporation of radiolabel followed CK activity and not CK copy number. Further, [alpha(32)P]ADP and [gamma(32)P]ATP incorporated P-32 into control brain and purified brain CK equally well, indicating that a mechanism different from gamma-phosphoryl transfer is involved in the enzymatic incorporation of radiolabel. Also, the level of abnormal partitioning of CK into AD brain pellet correlated with the decreased [P-32]8N(3)GTP photolabeling and abnormal partitioning of beta-tubulin, a protein known to be aberrantly modified in the AD brain. This indicates that a common chemistry is affecting both CK and tubulin in AD. (C) 1998 Elsevier Science B.V.