Document Detail

Characterization of a novel alpha-D-mannosidase from rat brain microsomes.
MedLine Citation:
PMID:  3902812     Owner:  NLM     Status:  MEDLINE    
A new alpha-D-mannosidase has been identified in rat brain microsomes. The enzyme was purified 70-100-fold over the microsomal fraction by solubilization with Triton X-100, followed by ion exchange, concanavalin A-Sepharose, and hydroxylapatite chromatography. The purified enzyme is very active towards mannose-containing oligosaccharides and has a pH optimum of 6.0. Unlike rat liver endoplasmic reticulum alpha-D-mannosidase and both Golgi mannosidases IA and IB, which have substantial activity only towards alpha 1,2-linked mannosyl residues, the brain enzyme readily cleaves alpha 1,2-, alpha 1,3-, and alpha 1,6-linked mannosyl residues present in high mannose oligosaccharides. The brain enzyme is also different from liver Golgi mannosidase II in that it hydrolyzes (Man)5GlcNAc and (Man)4GlcNAc without their prior N-acetylglucosaminylation. Moreover, the facts that the ability of the enzyme to cleave GlcNAc(Man)5GlcNAc, the biological substrate for Golgi mannosidase II, is not inhibited by swainsonine, and that p-nitrophenyl alpha-D-mannoside is a poor substrate provide further evidence for major differences between the brain enzyme and mannosidase II. Inactivation studies and the co-purification of activities towards various substrates suggest that a single enzyme is responsible for all the activities found. In view of these results, it seems possible that, in rat brain, a single mannosidase cleaves asparagine-linked high mannose oligosaccharide to form the core Man3GlcNAc2 moiety, which would then be modified by various glycosyl transferases to form complex type glycoproteins.
D R Tulsiani; O Touster
Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  The Journal of biological chemistry     Volume:  260     ISSN:  0021-9258     ISO Abbreviation:  J. Biol. Chem.     Publication Date:  1985 Oct 
Date Detail:
Created Date:  1985-11-29     Completed Date:  1985-11-29     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  2985121R     Medline TA:  J Biol Chem     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  13081-7     Citation Subset:  IM    
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MeSH Terms
Brain / enzymology*
Drug Stability
Endoplasmic Reticulum / enzymology
Golgi Apparatus / enzymology
Hydrogen-Ion Concentration
Immunosorbent Techniques
Mannose / metabolism
Mannosidases / antagonists & inhibitors,  isolation & purification,  metabolism*
Microsomes / enzymology*
Oligosaccharides / metabolism
Polysaccharides / metabolism
Rats, Inbred Strains
Substrate Specificity
Grant Support
Reg. No./Substance:
0/Oligosaccharides; 0/Polysaccharides; 31103-86-3/Mannose; EC 3.2.1.-/Mannosidases; EC

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