Altered serum alpha-D-mannosidase activity in mucolipidosis II and mucolipidosis III. |
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Authors: | B C Kress A L Miller |
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Institution: | Department of Neurosciences, School of Medicine University of California, San Diego La Jolla, California 92093, USA |
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Abstract: | Normal human serum contains at least three forms of α-D-mannosidase: an acidic form which has a pH optimum of 4.25, is inhibited by Co2+ and is thermostable; an intermediate form, which has a pH optimum of 5.6–5.7, is stimulated by Co2+ and is heat labile at 50°C; and a neutral form with a pH optimum of 6.0–6.5. In Mucolipidosis II and III sera, the acidic α-mannosidase activity persists while the intermediate activity is absent or altered. Heating the serum does not affect the pH activity curve, the electrofocusing profile or the response to Co2+ of α-mannosidase. During heat inactivation at 55°, 90–100% of the pH 5.6 α-mannosidase activity is lost in normal sera while less than 40% is lost from ML sera. The effect on sera from ML obligate heterozygotes is intermediate. The absent or altered intermediate mannosidase may be responsible for aberrant biochemical properties reported for other glycosidases in Mucolipidosis II and Mucolipidosis III. |
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