These experiments examined effects of cholesterol oxidation on Ca2++Mg2+-ATPase activity, Na++K+-ATPase activity, and membrane structure of brain synaptic plasma membranes (SPM). Cholesterol oxidase [E.C.184.108.40.206 fromBrevibacterium sp.] was used to oxidize cholesterol. Two cholesterol pools were identified in synaptosomal membranes based on their accessibility to cholesterol oxidase. A rapidly oxidized cholesterol pool was observed with a1t12 of 1.19±0.09 min and a second pool with a2t12 of 38.30±4.16 min. Activity of Ca2++Mg2+-ATPase was inhibited by low levels of cholesterol oxidation. Ten percent cholesterol oxidation, for example, resulted in approximately 35% percent inhibition of Ca2++Mg2+-ATPase activity. After 13% cholesterol oxidation, further inhibition of Ca2++Mg2+-ATPase activity was not observed. Activity of Na++K+-ATPase was not affected by different levels of cholesterol oxidation (5%-40%). SPM interdigitation was significantly reduced and fluidity was significantly increased by cholesterol oxidation. The relatiobship observed between SPM interdigitation and Ca2++Mg2+-ATPase activity was consistent with studies using model membranes . Brain SPM function and structure were altered by relatively low levels of cholesterol oxidation and is a new approach to understanding cholesterol dynamics and neuronal function. The sensitivity of brain SPM to cholesterol oxidation may be important with respect to the proposed association between oxygen free radicals and certain neurodegenerative diseases.
Bibliographical noteFunding Information:
This work was supportedin part by NIH GrantsA G-11056,A A-07292( W.G.W.) and by the Medical Research Servicea ndthe GeriatricR esearchE, ducationa ndClinical Centero f the Departmenotf VeteransA ffairs.
- Cholesterol oxidase
- Cholesterol oxidation
- Synaptic plasma membrane