Leucine Aminopeptidase (Aminopeptidase-I) N-Acetyl-Beta-Hexosaminidase And Lysosomes In The Mussel Mytilus-Edulis-L In Response To Salinity Changes

The intracellular distribution of aminopeptidase-I in the intestinal and digestive cells of Mytilus edulishas been shown to be the same as the lysosomal marker enzymes β-glucuronidase and N-acetyl-β-hexosaminidase. Activity for these enzymes was also associated with the intestinal apical cytoplasm and microvillous border where there was pronounced staining for aminopeptidase-I. Experimental alterations of salinity induced changes in both microdensitometrically and spectrophotometrically determined aminopeptidase-I activity, as an increase with raised salinity and a decrease with lowered salinity. Lysosomal hexosaminidase showed similar changes in activity with altered salinity. Cytochemically determined lysosomal stability was also responsive to salinity changes, indicative of alterations in lysosomal functional capability. The lysosomal distribution of aminopeptidase-I is discussed in terms of the function of lysosomes in intracellular protein turnover, their high concentrations of free amino acids, and the possible roles which these might play in intracellular osmoregulation in response to salinity change.

Identification of the region of non-A beta component (NAC) of alzheimer's disease amyloid responsible for its aggregation and toxicity

The non-beta-amyloid (Aß) component of Alzheimer's disease amyloid (NAC) and its precursor a-synuclein have been linked to amyloidogenesis in several neurodegenerative diseases. NAC and a-synuclein both form ß-sheet structures upon ageing, aggregate to form fibrils, and are neurotoxic. We recently established that a peptide comprising residues 3±18 of NAC retains these properties. To pinpoint the exact region responsible we have carried out assays of toxicity and physicochemical properties on smaller fragments of NAC. Toxicity was measured by the ability of fresh and aged peptides to inhibit the reduction of the redox dye 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) by rat pheochromocytoma PC12 cells and human neuroblastoma SHSY-5Y cells. On immediate dissolution, or after ageing, the fragments NAC(8±18) and NAC(8±16) are toxic, whereas NAC(12±18), NAC(9±16) and NAC(8±15) are not. Circular dichroism indicates that none of the peptides displays ß-sheet structure; rather all remain random coil throughout 24 h. However, in acetonitrile, an organic solvent known to induce ß sheet, fragments NAC(8±18) and NAC(8±16) both form ß-sheet structure. Only NAC(8±18) aggregates, as indicated by concentration of peptide remaining in solution after 3 days, and forms fibrils, as determined by electron microscopy. These findings indicate that residues 8±16 of NAC, equivalent to residues 68±76 in a-synuclein, comprise the region crucial for toxicity.