Mannosidase tissues

In mouse liver and kidney and in rat liver, a-D-mannosidase activity appeared to be equally distributed between the two cytoplasmic-granule fractions. With mouse spleen and cancer tissue, a considerable proportion of the enzyme was found free in the cytoplasm. Rat spleen, on the other hand, lacked this cytoplasmic fraction. Inasmuch as the enzyme within the cytoplasmic granules was not fully active in a sucrose homogenate until the membranes had been disintegrated, a-D-mannosidase conforms to the definition of a lysosomal hydrolase. 

The theory has been advanced that there exists in the cell a particulate structure somewhat smaller than the mitochondrion, the lyso-some, that contains certain autolytic enzymes in a latent situation. The lysosome theory55,56 is very largely based upon measurements made in sucrose homogenates of rodent liver. Although the results for a-D-mannosidase in this tissue (see Table IV) are not incompatible with the theory, the results for other tissues do not always conform to it. In particular, the contrast between mouse and rat spleen argues against a universal single particle to which a-D-mannosidase is confined. Apart from the results quoted in Table IV, not much work has been done on the intracellular location of a-D-mannosidase. 

Although the a-D-mannosidase activity of several different organs in mammals has been found to alter under a variety of conditions (see Section 11,1 p. 402),11,12-14,28,28 the most striking changes are those produced by sex hormones in the epididymis and uterus.26,28 In rats and mice, a-D-mannosidase activity in the epididymis increases with the age of the animal, up to maturity orchidectomy causes a dramatic fall in the enzyme activity of the adult tissue (up to 100-fold), but activity can be partially restored by the administration of testosterone. Ovariectomy results in a 10-fold fall in the activity of a-D-mannosidase in mouse uterus, and this is completely reversed by estrone. 

One of the most interesting aspects of the changes in a-D-man-nosidase activity known to occur in vivo is the possible relationship with changes in zinc concentration in the tissues. In the case of rat epididymis, changes in enzyme activity have been monitored in parallel with measurements of zinc content.26 There was a positive correlation between the two variables, as both increased with age. The drop in a-D-mannosidase activity resulting from orchidectomy was accompanied by a 4-fold fall in the zinc content of epididymis, but the restoration of enzyme activity produced by subsequent injection of testosterone was not reflected in a detectable rise in the proportion of zinc. 

In zinc-deficient rats, the zinc content of the epididymis was only about half the normal value,28,87 and the level of a-D-mannosidase activity was also little over half the value usually observed.26 However, the zinc concentration of the tissue was still in vast excess over that required for stoichiometric combination with the enzyme protein, calculated on any probable estimate of its specific activity and molecular weight (see Section III,5 p. 433). 

In a tissue having a high a-D-mannosidase activity, such as the epididymis, zinc may be needed in great excess to lessen dissociation of the catalytically active protein-zinc complex and the consequent displacement of Zn2+ by other bivalent cations (such as Cd2+) to yield... 

D-galactosidase nor / -D-glucosidase plays an important role in shortterm growth promoted by auxin or acid in oat coleoptiles, Greve and Ordin245 purified, and characterized, the wall-bound a-D-mannosidase of this tissue. 

There have been only a few kinetic studies on plant /3-D-manno-sidases, because of the apparently limited distribution of this enzyme in various species, and also because of the paucity of attempts at purification. The enzyme from malted barley has been purified 41-fold by fractionation with ammonium sulfate, and chromatography302 on Biogel P-100, DEAE-cellulose, and CM-cellulose. Some properties of /3-D-mannosidases from various tissues are summarized in Table II. 

Fig. 1. Proposal for the biosynthesis of N-linked oligosaccharides in connective tissue from Lymnaea stagnalis [59]. The compounds are represented by short-hand symbolic notation as explained in the figure. Solid arrows indicate steps verified by experiments and dotted arrows indicate probable steps [57-60]. Man II represents a-mannosidase II abbreviations of other enzymes are explained in the text. Boxed structures are presented as formulae in Scheme 4, and have been isolated from L. stagnalis He [22,23].

Tremblay LO, Campbell Dyke N, Herscovics A. Molecular cloning, chromosomal mapping and tissue-specific expression of a novel human alphal,2-mannosidase gene involved in A-glycan maturation. Glycobiology 1998 8 585-595. 

Acid a-D-mannosidase (mol. wt. 1.84 X10, 8.1 X 10, and 4.54 x lO" by gel filtration, urea- el filtration, and sodium dodecyl sulphate-polyacrylamide gel electrophoresis, respectively pi 5.9 pH optimum 4.2) was purified more than 2000-fold — via conventional techniques, affinity chromatography on immobilized concanavalin A, and Pevikon electrophoresis — from porcine kidneys. The final product contained the multiple forms A and B and had a quaternary structure. The immunoglobulin fraction of rabbit antiserum against the pure a-D-mannosidase leads in immunodiffusion and precipitation experiments to precipitation not only with a-D-mannosidase from porcine tissues but also (though with lower affinity) from bovine liver and human placenta, urine, and skin fibroblasts. 

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 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. ... 

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