PRIMARY STRUCTURE OF THE CYTOSOLIC BETA-GLUCOSIDASE OF GUINEA-PIG LIVER

The cytosolic beta-glucosidase (EC 3.2.1.21) present in the livers of mammalian species is distinguished by its broad specificity for sugars and its preference for hydrophobic aglycones. We purified the cytosol ic beta-glucosidase from guinea pig liver and sequenced 142 amino acid residues contained within 12 trypsin digest fragments. Using degenera te oligonucleotide primers deduced from the peptide sequences, a 622 b p cytosolic beta-glucosidase cDNA was amplified by reverse-transcripta se PCR, using total guinea pig liver RNA as template. The 'rapid ampli fication of cDNA ends (RACE)' method [Frohman (1993) Methods Enzymol. 218, 340-356] was used to synthesize the remaining segments of the ful l-length cDNA. The complete cDNA contained 1671 nucleotides with an op en reading frame coding for 469 amino acid residues. The amino acid se quence deduced from the cDNA sequence included the amino acid sequence s of all 12 trypsin digest fragments derived from the purified enzyme. Amino acid sequence analysis indicates that the guinea pig liver cyto solic beta-glucosidase is a Family 1 beta-glycosidase and that it is m ost closely related to mammalian lactase-phlorizin hydrolase. These re sults suggest that the cytosolic beta-glucosidase and lactase-phlorizi n hydrolase diverged from a common evolutionary precursor.