Easily autooxidizable catecholamines are known to generate reactive radicals and H2O2 under aerobic conditions due to their inherent redox properties. Consequently, catecholaminergic neurons are inherently subjected to high oxidative stress and free radical damage. The degneration of catecholaminergic neurons in aging and central nervous system diseases such as Parkinson's Disease, as well as in the use of illicit drugs such as amphetamines have been attributed to the catecholamine mediated excessive production of oxygen free radicals and/or H2O2 in the affected areas of the brain. Although, most of the reactive radical species and oxidants are effectively scavenged by enzymatic defense mechanisms and by cellular oxidants, their excessive generation may lead to extensive cellular damage. Presence of high concentrations of ascorbate (Asc), an intricate ATPase drive, b561-mediated, Asc regenerating system (ARS), and an efficient catecholamine uptake mechanism together with the absence of antioxidants such as glutathione in catecholamine storage vesicles suggest that, in addition to providing electrons for dopamine beta-monooxygenase (DbetaM) and peptidyl alpha- hydroxylating monooxygenase (PHM) reactions, Asc must also play a key role in the protection of catecholaminergic neurons from catecholamine induced free radical damage. Therefore, the malfunctioning of proton translocating ATPase, ARS, or monoamine transporter could result in high oxidative stress leading to an exponentially propagating cascade of radical generation and extensive cellular damage. Despite this convincing evidence, the biochemical mechanisms that my integrate the pathological features in catecholaminergic neurons have not been fully explored. Thus, a more precise description of (a) the biochemical steps in catecholamine metabolism and (b) the role of antioxidants in protecting catecholamines from oxidation, consequently relieving oxidative stress could be a significant advancement in our understanding of the dysfunction of catecholaminergic neurons. The overall objective of the proposed studies is to examine the functional coupling of the monoamine transporter, proton translocating ATPase, ARS, and DbetaM at the molecular level using multidisciplinary approaches using chromaffin granules and granule ghosts as a model. With a better understanding of the functional coupling of these proteins, the role of these proteins in protecting catecholamine storage vesicles from oxidative stress as well as the effect of oxidative stress on their individual and coordinated functions will be examined.
