Processing and metabolism of beta-amyloid precursor protein (APP) and generation of a variety of beta-amyloid (Abeta) peptides in the human brain is essentially associated with pathophysiology of Alzheimer's disease (AD). APP degradation activity of the 68 kDa serine protease, which was originally prepared from familial AD lymphoblastoid cells and harbors beta-secretase-like activity, was analyzed by Western blot using anti Abeta 1/40 antibody and anti APP cytoplasmic domain (CT) antibody. Native lymphocyte APP (LAPP) prepared from normal or AD-derived lymphoblastoid cells was degraded by the protease, generating a 16 kDa Abeta-bearing C-terminal fragment of APP. N-terminal amino acid sequencing of the fragment indicated that the protease cleaves LAPP at the Abeta-N-terminus. When the LAPP was treated with chondroitinase ABC prior to proteolysis, the activity to generate the fragment was inhibited, but pretreatment with heparitinase resulted in no effect. Native hippocampal APP prepared from normal brain, however, did not generate the 16 kDa peptide by the protease treatment. These results suggest that the process of APP degradation and Abeta-peptides generation, including beta-secretase activity, is associated with tissue specificity of both APP substrate and proteases. They also indicate that sulfated glycoconjugates attached to a portion of APP isoforms may play a role as a molecular determinant in the proteolysis.
Under conditions of experimental myocardium infarction caused in dogs by ligation of the anterior descending branch of the left coronary artery, the activity of alpha-ketoglutarate dehydrogenase and succinate dehydrogenase in mitochondria of the cortex, cerebellum and medulla ablongata lowers most intensively on the first and fifth day after the appearance of acute myocardium infarction. Activation of the most important enzymes of the pentose-phosphate cycle (glucose-6-phosphate dehydrogenase and transketolase) which is clearly pronounced on the fifth day is observed in the mentioned sections. In the authors' opinions the above changes in the activity of the enzymes are due to the brain hypoxia which may be the main reason of disturbance in the function of the central nervous system under this disease.
A previous study, in which a lysed fraction was used with endogenous phospholipids as substrate, revealed age-related changes in PA and PIP2 formation but not in PIP formation (Bothmer et al., Neurochem. Int. 21, 223-228, 1992). To rule out the influence of substrate availability in the present study, the effect of age on PI kinase, PIP kinase and DAG kinase activities was studied with exogenous phospholipids as substrate in the cerebral cortex from 8-month-old, 14-month-old and 26-month-old Brown Norway rats. PI kinase activity was predominantly located in a tight membrane-bound protein fraction, DAG kinase activity in cytosolic and loosely membrane-bound protein fractions, and PIP kinase activity was present in all three protein preparations. The effects of age were limited to a small increase in kinase activity in the tight membrane-bound protein fraction in 14-month-old and 26-month-old rats compared to 8-month-old rats, and a 10% decrease in PIP kinase activity in the cytosolic protein fraction in 14-month-old and 26-month-old rats compared to 8-month-old rats. DAG kinase activity showed no age-related changes. In conclusion, one should take care in comparing rat aging with human aging as PI kinase activity shows an age-related decline in human brain cortex (Jolles et al., J. Neurochem. 58, 2326-2329, 1992). Furthermore, previously reported decreases in PA formation rates in rat brain are probably not due to changes in DAG kinase itself but to changes in DAG availability, although further experimental evidence is needed to confirm this conclusion.
The range of the Na+, K(+)-ATPase functional stability in microsomal fraction of rat brain cortex under long-term chronic ethanol (15%, v/v) consumption was ascertained. The enzyme activity decreased only after 15 months of alcoholisation on the background of the stable structural membrane characteristics (on the basis of the intrinsic and 1-anilinonaphthalene-8-sulfonate fluorescence parameters) and SH-content in postmitochondrial supernatant. The cellular homeostatic mechanisms under ethanol effect are discussed.