Purification, characterization and N-terminal sequence analysis of betel leaf (Piper betle) invertase

Abstract

The present study is the first report describing the purification, enzymatic properties and N-terminal amino acid sequence of a native invertase in betel leaf. The invertase was purified as a monomeric glycoprotein of molecular mass (Mr) 68 kDa. The enzyme was capable to attack β-fructofuranoside linkages from the fructose end of sucrose, raffinose and stachyose indicating it as an authentic β-D-fructofurano-sidase with high specificity for sucrose (Km 4.83 mM). The maximum activity was detected at pH 5.2 and 37 °C. Glucose and fructose showed typical inhibitory effect on the enzyme activity where as lectin was found to be effective activators of the enzyme. Significant inhibition by heavy metal ion Hg2+ and sulf-hydryl group modifying agents suggesting that free sulfhydryl group containing amino acid, cysteine is necessary for the catalytic activity of the invertase. A BLAST search of the N-terminal amino acid sequence of betel leaf invertase showed significant homology with the homologous invertases in database.