beta-D-Mannosidase activity in selected normal adult, neonatal and foetal goat tissues and in tissues from animals affected with caprine
beta-mannosidosis was examined with the use of 4-methylumbelliferyl beta-D-
mannopyranoside as substrate. The
enzyme in normal adult thyroid, kidney and brain exhibited a sharp unimodal pH optimum at pH 5.0, whereas the
enzyme in both normal adult and mutant liver exhibited broad pH ranges of activity (pH 4.5-8.0). No residual
enzyme was detectable in mutant kidney or brain; in contrast, residual activity in mutant liver was 52% of that in a neonatal control.
Concanavalin A-Sepharose 4B (
Con A-Sepharose) fractionation of normal adult liver
beta-D-mannosidase resolved the
enzyme into an unbound (non-lysosomal) from (52%) with a broad pH range of activity (pH 4.5-8.0) and a bound (lysosomal) form (48%) with a sharp pH optimum of 5.5. The
enzyme in mutant liver consisted entirely of the unbound (non-lysosomal) form.
Beta-D-Mannosidase activity in normal adult thyroid, kidney and brain was resolved by chromatofocusing into two major
isoenzymes, with pI 5.5 and 5.9, and traces of a minor
isoenzyme, with pI 5.0. In normal adult liver the
enzyme was also resolved into three
isoenzymes with similar pI values; however, that with pI 5.0 predominated. The predominant form of the
enzyme in 60-day-foetal liver was bound by Con A, exhibited a unimodal pH optimum (5.0) and was resolved into two
isoenzymes, with pI 5.4 and 5.8; only traces of an
isoenzyme with pI 5.0 were detectable. Total hepatic
beta-D-mannosidase activity increased progressively towards adult values during the last 90 days of gestation as a result of increasing non-lysosomal
isoenzyme activity (pI 5.0). Lysosomal
beta-D-mannosidase was shown to occur in all normal goat tissues studied as multiple
isoenzymes, which are genetically and developmentally distinct from the non-lysosomal
isoenzyme occurring predominantly, if not exclusively, in liver.