Sialidases of Protozoa and Invertebrates

Sialidases have been found in several protozoan species including Try-panozoma cruzi (Pereira, 1983 Pereira and Hoff, 1986), T. vivax (Esievo, 1983), T. brucei (Engstler et al., 1992), Naegleria fowleri (Eisen and Franson, 1987), and Acanthamoeba (Pellegrin et al., 1991). Among them, the enzyme in T. cruzi, 

cruzi sialidase may play an important role in the infectivity of the para- 

Sialidase activity has been detected in certain invertebrate species. A recent study has demonstrated that the leech Macrobdella decora contains not only an ordinary sialidase, but also a novel sialidase which releases 2,7-anhydro-a-A-acetylneuraminic acid from various sialoglycoconjugates (Li et al., 1990). The purified enzyme has a molecular mass of 84 kDa and shows strict specificity for the a2-3 linkage in Neu5AcLac and gangliosides the enzyme does not cleave the a2-6 and a2-8 linkages (Chou et al., 1992). The mechanism of action of this enzyme is unknown. 

A soluble sialidase in the starfish Asterias rubens has been purified to homogeneity (Schauer and Wember, 1989). This enzyme has a molecular mass of 230 kDa with four identical subunits and preferentially cleaves a2-3-linked sialic acids in various substrates. Another enzyme in the hepatopancreas from the shrimp Penaeus japonicus has been shown to be a 32-kDa protein which binds P-galactosidase in vitro. No protective protein has been detected for this enzyme (Chuang and Yang, 1990) (see Section 5.1 for protective protein). 

Recent studies have shown that the lysosomal sialidase exists as a complex with P-galactosidase, protective protein, and other proteins including V-ace- 

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