Multiple α-mannosidase activities in mammalian tissues as shown by metal-ion activation

Abstract

1. Four different types of alpha-mannosidase activity were shown to occur in several tissues from the rat. There is the Zn2+-dependent enzyme, active at acidic pH, and three enzymes that are active near to neutral pH. 2. The 'neutral' enzymes are activated by Fe2+, Co2+ or Mn2+. 3. Optimum activities for these three enzymes are shown at pH values of 5.2, 6.5 and 7.3. The activity at pH6.5 is the only one evident without metal-ion activation, but activity is enhanced by all three metal ions. The activity at pH 5.2 is seen only in the presence of Fe2+ or Co2+, and the activity at pH7.3 is seen only in the presence of Co2+ or Mn2+ and in a non-chelating buffer medium. 4. The pH6.5-active enzyme is inactivated by EDTA, but activity is restored by excess of metal ion. 5. The enzymes differ markedly in their stability. The pH6.5-active enzyme is very labile and the pH7.3-active enzyme is the most stable. 6. Tissue preparations vary widely in their activity at pH6.5, but where activity is low it can be increased by incubation with one of the activating metal cations. 7. All the enzymes active at neutral pH are inhibited by heavy-metal ions and stabilized to some extent by thiol groups.

Effect of swainsonine on rat epididymal glycosidases

“…However, in rat epididymal tissue, only lysosomal a-Dmannosidase, with a pH optimum of 4-5 (Snaith & Levvy, 1969), and cytosolic a-D-mannosidase with a neutral pH optimum (Snaith, 1977) have been identified. In bovine tissue, the acidic enzyme activity was highest in seminal plasma and the epididymis where the activity seems to be mainly in secretory form; the neutral a-mannosidase activity was high in epididymal homogenate and in epididymal and ejaculated spermatozoa (Jauhiainen & Vanha-Perttula, 1987).…”

Comparative Physical, Kinetic and Immunologic Properties of the Acidic and Neutral α-D-Mannosidase Isozymes from Human Liver

“…Support for this hypothesis will require homogenous isozyme preparations. It is of note that Smith (18) has recently shown that homogenous jack bean a-mannosidase is a zinc metalloenzyme, and that rat liver neutral a-mannosidase was stimulated by cobalt and ferrous ions (19).…”

Molecular characterization of Capra hircus lysosomal α-mannosidase and potential mutant site for the therapy of locoweed poisoning.

“…This cleavage pattern appears to vary in different organisms . LAM is involved in N-glycan processing pathways and is associated with endoplasmic reticulum associated protein degradation process (Snaith, 1977;Uno et al, 2010). It is an exoglycosidase that hydrolyses all known α (axial)-mannosidic linkages on mannose-glycans originating from unfolded or endocytosed proteins (Snaith, 1975;Merkle et al, 1997;Athanasopoulos et al, 2005).…”

“…It is an exoglycosidase that hydrolyses all known α (axial)-mannosidic linkages on mannose-glycans originating from unfolded or endocytosed proteins (Snaith, 1975;Merkle et al, 1997;Athanasopoulos et al, 2005). LAM have been isolated and well studied from various animals, plants, and microorganisms sources, such as rat, jack bean, and Aspergillus phoenicis etc (Snaith, 1975;Snaith, 1977;Athanasopoulos et al, 2005). In humans, cattle, cat and guinea pig, the lack of LAM activity causes the autosomal recessive disease α-mannosidosis (Michalski & Klein, 1999).…”