Aldolase
This enzyme belongs to the class I aldolases (Misset and Opperdoes, 1984) that catalyse the reversible cleavage of the fructose 1,6-bisphosphate via the formation of a Schiff-base into the trioses DHAP and GA3P without the need of a divalent metal ion. In the bloodstream form it is almost completely found in the glycosome, where it represents 34% of all the protein, or 1700 molecules per organelle and it represents 1.2% of the total trypanosome protein. The trypanosome enzyme is a homotetrameric protein with a molecular mass of 157 000 and a pI of 9. Two almost identical tandemly repeated genes encode a polypeptide of 371 amino acids with a calculated subunit mass of 40 940 (Clayton, 1985; Marchand et al., 1988). The enzyme has an extension at its N-terminus of about 10 amino acids that codes for a type 2 peroxisomal targeting signal. The enzyme is between 45 and 47 % identical to other eukaryotic aldolases and displays the typical properties of other class I aldolases (Misset and Opperdoes, 1984; Callens et al., 1991b). T. brucei aldolase has been studied in detail (Callens et al., 1991b) and it has been overexpressed to high levels (Chevalier et al., 1995). A low degree of phosphorylation of the enzyme at the level of a serine residue has been reported, but the function of this phosphorylation remains to be determined (Clayton and Fox, 1989).