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Substrate specificity of human liver neutral alpha-mannosidase
S al Daher1, R De Gasperi, P Daniel
1Division of Biochemistry and Metabolism, Institute of Child Health (University of London), U.K.
The Biochemical Journal
|August 15, 1992
Summary
Human liver neutral alpha-mannosidase modifies high-mannose oligosaccharides via distinct pathways. This enzyme
Area of Science:
- Biochemistry
- Glycobiology
- Enzymology
Background:
- Human liver neutral alpha-mannosidase plays a role in oligosaccharide metabolism.
- High-mannose oligosaccharides are involved in various cellular processes.
- Understanding enzyme specificity is crucial for elucidating metabolic pathways.
Purpose of the Study:
- To investigate the digestion pathways of radiolabeled natural oligosaccharide substrates by human liver neutral alpha-mannosidase.
- To determine the specific hydrolysis routes and products generated by the enzyme.
- To compare these pathways with known processing and lysosomal catabolic pathways.
Main Methods:
- Digestion of radiolabeled high-mannose oligosaccharides (Man9GlcNAc, Man8GlcNAc) using human liver neutral alpha-mannosidase.
- Analysis of hydrolysis products using high-performance liquid chromatography (HPLC) and high-performance thin-layer chromatography (HPTLC).
Main Results:
- Man9GlcNAc and Man8GlcNAc are hydrolyzed via distinct non-random routes to Man6GlcNAc, then slowly to Man5GlcNAc.
- Specific alpha(1----2)-linked mannose residues and the core alpha(1----3)-mannosidic linkage show resistance to hydrolysis.
- The key processing intermediate is not produced, but Man beta(1----4)GlcNAc is formed via core structures.
Conclusions:
- Human liver neutral alpha-mannosidase exhibits precise specificity towards high-mannose oligosaccharides.
- The enzyme's distinct hydrolysis pathways differ from processing and lysosomal pathways.
- This specificity suggests a role in the cytosolic modification of high-mannose structures.