Kinetics and Regulation Studies of the Production of β-Galactosidase from Kluyveromyces marxianus Grown on Different Substrates
Muhammad Ibrahim Rajoka*, Samia Khan and Riaz Shahid
National Institute for Biotechnology and Genetic Engineering, P.O. Box 577, Jhang Road, Faisalabad, Pakistan
Article history:
Received: May 16, 2003
Accepted: November 10, 2003
Key words:
β-galactosidase; Kluyveromyces marxianus; lactose, galactose, cellobiose, xylose and glucose as substrates
Summary:
Lactose-intolerance is manifested in 50 % of the world’s population. This can be remediated by removing lactose from the diet or converting it into glucose and galactose with β-galactosidase (EC 3.2.1.23). In this work, batch production of this enzyme in the presence of lactose, galactose, cellobiose, xylose, arabinose, sucrose and glucose was investigated using Kluyveromyces marxianus in shake flask culture studies. Substrate type and temperature were the independent variables that directly regulated the specific growth and β-galactosidase production rates. Lactose (2 %) supported the maximum specific product yield (YP/X), followed by galactose, sucrose, cellobiose, xylose, arabinose and glucose. Its synthesis was regulated by an induction and a growth-dependent repression mechanism. The optimum temperature for the production was found to be 35–37 °C. The highest volumetric productivity of enzyme (80.0 IU/L/h) occurred on lactose-corn steep liquor medium. This was significantly higher than the calculated values reported in the literature. Thermodynamic studies revealed that the cells provided a defence mechanism against thermal inactivation. The enzyme was stable at 60 °C and pH=5.0–7.0, and it may find application in commercial lactose hydrolysis.
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