Mannosidases

Aspects of the affinity chromatography of a-D-mannosidase on glycose-substituted agaroses have been investigated. a-D-Mannosidase activity can be detected in 

Suzuki, H. Kikucbi, C. Kato, Y. Horiuchi, K. Tomita, and Y. Hashimoto, Biochem. Pharmacol., 1977, 26, 881. 

Two forms of a-D-mannosidase, each having a neutral pH optimum, have been found in human sera they can be distinguished by molecular-sieve chromatography, ion-exchange chromatography, or affinity chromatography on immobilized concanavalin The properties of the enzymes were compared with those of the acidic a-D-mannosidase. 

An a-D-mannosidase (acid pH optimum) that is Zn -dependent and three other a-D-mannosidase activities (neutral pH optima) have been found in the tissues of rats. The enzymes most active at a neutral pH value were inhibited by heavy-metal ions and were stabilized, to some extent, by thiols. The reversible effects of Fe , Co and Mn ions and H edta on the activity of these enzymes were investigated. Tissue preparations varied widely in the levels of the enzymes most active at pH 6.5, although latent enzymic activity was released on incubation with activating metal ions. 

The cytosolic form of the a-D-mannosidase from rat liver has been purified (1.2 X lO -fold) using D-mannopyranosylamine and 1,4-dithioerythritol as stabilizers. The enzyme (mol. wt. 3.72—4.90 x 10 , pH optimum 5.5—5.9, for 

The activities and properties of an a-D-mannosidase of diploid Wl-38 fibroblasts from embryonic human-lung tissues have been reported. Mannosidosis is a genetic disorder that can be recognized by a deficiency of a specific a-D-mannosid-ase in cultured fibroblasts.  

A single passage of a crude extract of human placenta through a column of concanavalin A immobilized on macroporous agarose effected the purification of an a-D-mannosidase by 300-fold. The nature of the interaction with concanavalin A indicated that the a-D-mannosidase is a glycoprotein. 

The distribution and concentration of a-D-mannosidase in cellular fractions of neutrophils and eosinophils of equine blood have been reported. The latency, pH requirements, and inhibition response to heparin of the enzyme were examined. 

The effects of streptozotocin-induced diabetes on the levels of a-D-mannosidase activities of various organs and sera of rats have been studied.  

The a- and jS-D-mannosidase activities of fowl semen have been investigated. The purification and properties of a purified jS-D-mannosidase from malted barley have been reported.  

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Inhibition of D-Mannosidases and D-Glucosidases by Swainsonine and Castanospermine, Respectively... 

A case similar to the slow, practically irreversible inhibition of jack bean a-D-mannosidase by swainsonine is represented by the interaction of castanospermine with isomaltase and rat-intestinal sucrase. Whereas the association constants for the formation of the enzyme-inhibitor complex were similar to those of other slow-binding glycosidase inhibitors (6.5 10 and 0.3 10 M s for sucrase and isomaltase, respectively), the dissociation constant of the enzyme-inhibitor complex was extremely low (3.6 10 s for sucrase) or could not be measured at all (isomaltase), resulting in a virtually irreversible inhibition. Danzin and Ehrhard discussed the strong binding of castanospermine in terms of the similarity of the protonated inhibitor to a D-glucosyl oxocarbenium ion transition-state, but were unable to give an explanation for the extremely slow dissociation of the enzyme-inhibitor complex. 

Group (c), a-D-mannosidase from jack beans and from almonds, and a-D-galactosidase from coffee beans, showed no inactivation. The results with these enzymes can possibly be explained by the formation of a (weak) non-covalent complex in which glycosylation is too slow to cause inactivation within the time period of measurements, or, less likely, rapid hydrolysis of the glycosyl-enzyme intermediate. 

The protein-bound oligosaccharide is then partially processed by glucosidases and mannosidases if no additional sugars are added, this results in a high-mannose chain. 

For example, prior action of GIcNAc transferase I is necessary for the action of Golgi a-mannosidase II. 

HEMPAS (MIM 224100) Abnormalities in certain enzymes (eg, mannosidase II and others) involved in the biosynthesis of N-glycans, particularly affecting the red blood cell membrane. 

Colgate, S. M., Dorling, P. R. and Huxtable, C. R. 1979. A spectroscopic investigation of swainsonine an a-mannosidase inhibitor isolated from Swainsona canescens. Austral. J. Chem. 32 2257-2264. 

Base-catalyzed nitromethane cyclization of the dialdehyde generated by periodate oxidation of 1,2-O-cyclohexylidene-myo-inositol affords the nitrodiol with 1,4/2,3,5-configuration. This is converted into the a-mannosidase inhibitor, mannostatin A (Eq. 3.60).98... 

S. Singh, M. Scigelova, and D. H. G. Crout, Glycosidase-catalysed synthesis of mannobioses by the reverse hydrolysis activity of alpha-mannosidase Partial purification of alpha-mannosidases from almond meal, limpets and Aspergillus niger, Tetrahedron Asymmetry, 11 (2000) 223-229. 

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