pastoris extracellular β-D-galactosidase production for a thermostable enzyme from Alicyclobacillus acidocaldarius IWP-2 mw [23]. There are several examples of cold active β-D-galactosidases isolated from Pseudoalteromonas

strains [5, 10, 11] and Arthrobacter strains [7–9, 12, 13] with molecular mass above 110 kDa of monomer and forming an active enzyme of over 300 kDa. Most of them belong to the family 42 β-D-galactosidases. However, the β-D-galactosidase belonging to family 2 obtained from the Antarctic Arthrobacter isolate appears to be one of the most cold-active enzymes characterized to date [8]. All of the known cold-adapted β-D-galactosidases, except two of them isolated from Planococcus sp. strains [4, 14] and from

Arthrobacter sp. 32c (this study), form very large oligomers and therefore are of minor interest in industrial application probably because of many problems in effective overexpression. The β-D-galactosidases isolated from psychrophilic Planococcus sp. strains have low molecular weight of about 75 kDa of monomer and about 155 kDa of native protein. The β-D-galactosidase isolated from Planococcus sp. L4 is particularly thermolabile, loosing its activity within only 10 min at 45°C [14] and therefore larger scale production of this enzyme by recombinant yeast strains PKC inhibitor cultivated at 30°C might be economically not feasible. Only the β-D-galactosidase from Planococcus sp. isolate SOS orange [4] displays interesting activity and might be considered in biotechnological production on a larger scale. In comparison with known β-D-galactosidases, the Arthrobacter Baf-A1 chemical structure sp. 32c β-D-galactosidase is a protein with a relatively low molecular weight.

Molecular sieving revealed that the active enzyme is a trimmer with a molecular weight of approximately 195 ± 5 kDa. Relatively low molecular weight of the protein did not interfere with extracellular production of the protein by P. pastoris. Therefore the constructed recombinant strains of P. pastoris may serve to produce the protein extracellularly with high efficiency and in a cheap way. The calculated production cost of 1 mg of purified β-D-galactosidase was estimated at 0.03 €. The same Pichia pastoris expression systems had been unsuccessfully used for extracellular expression of previously reported β-D-galactosidase from Pseudoalteromonas sp. 22b [10, 11]. This enzyme is much bigger than Arthrobacter sp. 32c β-D-galactosidase and forms a tetramer of approximately 490 kDa. It is worth noting that we have tried to secrete this enzyme with three different secretion signals (α-factor from Saccharomyces cerevisiae, glucoamylase STA2 from Saccharomyces diastaticus or phosphatase PHO5 from S. cerevisiae) with no success. It seems that the molecular mass of the desired recombinant protein is limited to extracellular production by P. pastoris host, whereas the used secretion signal is without any influence.