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Purification and biochemical characterization of a second type of neutral ceramidase from camel (Camelus dromedarius) brain
Ceramide occupies a central role in sphingolipid-mediated signalling events and therefore its level is tightly regulated by enzymes such as ceramidases. Ceramidases cleave the N-acyl linkage of ceramide, generating sphingosine and its subsequent product sphingosine-1-phosphate. Recently, we purified and characterized a neutral ceramidase (CBCDase I) with a molecular weight of 100kDa from camel brain. In the present study, we purified and characterized a second, more hydrophobic, neutral ceramidase from camel brain (CBCDase II). The purification protocol includes Triton X-100 extraction followed by a series of column chromatography. The purified CBCDase II appears as a single band corresponding to a molecular weight of ≈120kDa, showing maximum activity at pH 8.0. When compared with CBCDase I, CBCDase II is less glycosylated, and enzyme activity is inhibited by the metal ions Zn2+ and Cu2+, while Ca2+ stimulates activity. Phospholipids, such as phosphatidic acid, phosphatidylserine and phosphatidylglycerol, totally inhibited the enzyme activity, even at low concentrations. All thiol group-containing compounds that were tested inhibited the activity of CBCDase II. Nucleotides such as ADP, ATP, UMP and TMP inhibited enzyme activity even at low concentrations, whereas AMP inhibited the enzyme at higher concentrations only.