STABILITY AND ENZYMATIC PROPERTIES OF ?-GALACTOSIDASE FROM KLUYVEROMYCES FRAGILIS

Immobilisation of β-galactosidase within a lipid sponge phase: structure, stability and kinetics characterisation

In the formulation of an active enzyme enclosed in a matrix for controlled delivery, it is a challenge to achieve a high protein load and to ensure high activity of the protein. For the first time to our knowledge, we report the use of a highly swollen lipid sponge (L₃) phase for encapsulation of the large active enzyme, β-galactosidase (β-gal, 238 kDa). This enzyme has large relevance for applications in, e.g. the production of lactose free milk products. The formulation consisted of diglycerol monooleate (DGMO), and a mixture of mono-, di- and triglycerides (Capmul GMO-50) stabilised by polysorbate 80 (P80). The advantage of this type of matrix is that it can be produced on a large scale with a fairly simple and mild process as the system is in practice self-dispersing, yet it has a well-defined internal nano-structure. Minor effects on the sponge phase structure due to the inclusion of the enzyme were observed using small angle X-ray scattering (SAXS). The effect of encapsulation on the enzymatic activity and kinetic characteristics of β-galactosidase activity was also investigated and can be related to the enzyme stability and confinement within the lipid matrix. The encapsulated β-galactosidase maintained its activity for a significantly longer time when compared to the free solution at the same temperature. Differences in the particle size and charge of sponge-like nanoparticles (L₃-NPs) with and without the enzyme were analysed by dynamic light scattering (DLS) and zeta-potential measurements. Moreover, all the initial β-galactosidase was encapsulated within L₃-NPs as revealed by size exclusion chromatography.

Purification and properties of a β-galactosidase with potential application as a digestive supplement

Functional-based screening of crude beta-galactosidase activities from 42 yeast strains resulted in the selection of a single enzyme of potential interest as a digestive supplement. beta-Galactosidase produced by Kluyveromyces marxianus DSM5418 was purified to homogeneity by a combination of gel filtration, ion-exchange, and hydroxylapatite chromatographies. The denatured (123 kDa) and native molecular masses (251 kDa) suggest that the enzyme is a homodimer. The optimum pH and temperature of the purified enzyme were 6.8 and 37 degrees C, respectively. The unpurified beta-galactosidase in particular displayed a high level of stability when exposed to simulated intestinal conditions in vitro for 4 h. Matrix-assisted laser desorption ionization mass sectrometry analysis revealed that the enzyme's trypsin-generated peptide mass fingerprint shares several peptide fragment hits with beta-galactosidases from Kluyveromyces lactis. This confirms the enzyme's identity and indicates that significant sequence homology exists between these enzymes.

Effect of temperature and enzyme origin on the enzymatic synthesis of oligosaccharides

The aim of this research is to quantify the effect of temperature and enzyme origin on the enzymatic synthesis of oligosaccharides. Quantification of these effects is important because temperature and enzyme origin are important process parameters. A kinetic model was used to describe the concentrations in time. The kinetic parameters were determined by using data obtained in batch experiments at various temperatures (20, 30, 40, and 50 degrees C) and by using beta-galactosidases from Bacillus circulans, Aspergillus oryzae, Kluyveromyces lactis, and Kluyveromyces fragilis. The effect of temperature on the kinetic parameters could be described with the Arrhenius equation, except for the inhibition parameter. Slightly higher oligosaccharide yields were found at higher temperatures. However, the influence of the initial lactose concentration was much larger. The higher yield at higher temperatures is an additional advantage when operating at high initial lactose concentrations and consequently elevated temperatures. Clear differences between the beta-galactosidases were found concerning amount, size, and type of oligosaccharides produced. The beta-galactosidase from B. circulans produced the most abundant amount, the most different, and largest-sized oligosaccharides. The beta-galactosidases from Kluyveromyces spp. produced mainly trisaccharides. The kinetic parameters for the different enzymes were determined and differences were discussed.

Differences in the hydrolysis of lactose and other substrates by beta-D-galactosidase from Kluyveromyces lactis

The hydrolysis of o-nitrophenyl galactopyranoside and lactose by beta-D-galactosidase from Kluyveromyces lactis was enhanced by the addition of Mg2+ and Mn2+, but the rates of activation by each metal on both substrates were not the same. The Co2+, Zn2+, and Ni2+ activated the o-nitrophenyl galactopyranoside-hydrolyzing activity of the enzyme, but these same metals inhibited the lactose-hydrolyzing activity. The addition of Mg2+ and EDTA to the assay buffer increased the hydrolysis of o-nitrophenyl galactopyranoside and lactose at different rates. The responses of o-nitrophenyl galactopyranoside and lactose to the enzyme activity were different as a function of pH. The hydrolyzing activity toward both substrates also was influenced by the concentration of the phosphate in the assay buffer. However, the profile of the enzyme activity toward each substrate was different as a function of concentration. Because the assay of beta-galactosidase using o-nitrophenyl galactopyranoside is fast and convenient, the estimation of lactose-hydrolyzing activity of the enzyme has frequently been made based on the assay of o-nitrophenyl galactopyranoside hydrolysis. As shown in this study, a slight change in the conditions of the assay system and the enzyme application may cause changes in the ability of the enzyme to hydrolyze both lactose and o-nitrophenyl galactopyranoside. The change in o-nitrophenyl galactopyranoside-hydrolyzing activity is not always consistent with that of the lactose-hydrolyzing activity under the given condition, which may cause an inaccurate estimation of the enzyme activity in the enzyme preparation as well as in actual applications of the enzyme.

Purification and characterization of beta-galactosidase from a strain of Bacillus coagulans

beta-Galactosidase from B. coagulans strain L4 is produced constitutively, has a mol. wt. of 4.3 x 10(5) and an optimal temperature of 55 degrees C. The optimal pH at 30 degrees C is 6.0 whereas at 55 degrees C it is 6.5. The energy of activation of enzyme activity is 41.9 kJ/mol (10 kcal/mol). No cations are required. The Km with ONPG as substrate is 4.2-5.6 mM and with lactose is 50 mM. The Ki for inhibition by galactose is 11.7-13.4 mM and for dextrose is 50 mM. Galactose inhibited competitively while dextrose inhibited noncompetitively. The purified and unprotected enzyme is 70% destroyed in 30 min at 55 degrees C whereas in the presence of 2 mg/ml of BSA 42% of the activity is destroyed in 30 min at 55 degrees C. An overall purification of 75.3-fold was achieved.