Effects of Inhibitors on Kinetic Properties of Invertase from Saccharomyces cerevisiae

The understanding of the kinetic properties of invertase activity is that it is always produced during yeast fermentation and helps in the pretreatment and raw material preparation of ethanol production which usually uses molasses to achieve high efficiency of ethanol yield and productivity. Normally, the activity of enzymes is limited by many parameters including invertase. Thus, this research focused on some inhibitors that affected invertase activity produced from Saccharomyces cerevisiae, using cultivation on different carbon sources (pure sucrose solution and sugarcane molasses) compared with commercial invertase. Metal contamination from fertilizer during sugarcane cultivation has resulted in significant levels of calcium ions (Ca2+), potassium ions (K+), and magnesium ions (Mg2+) in harvested sugarcane at approximately 0.09, 0.18, and 0.05% (w/w), respectively. Consequently, harvested sugarcane and contamination from sugar processing were investigated in the current study, particularly the levels of the metal ions; Ca2+, K+, and Mg2+ that contaminated molasses. Moreover, the substrate and enzyme concentration were studied. The results showed that both crude invertases (sucrose and molasses invertase) had lower activity (lower V-max and higher K-m) than commercial invertase, probably due to enzyme impurities. Furthermore, the substrate and enzyme concentrations also affected the invertase activity, with increased values of V-0 and Q(p) indicating increased invertase activity at a sucrose concentration less than 100 g/L. Furthermore, increasing the crude invertase concentration had a negative effect on enzyme activity because of the greater interference by the impurities in sugar invertase compared to commercial invertase. Moreover, all metal ions were identified as competitive inhibitors and severely inhibited the activity of invertase at 0.6% (w/v) of metal ion concentration, especially with Ca2+ contamination.