SDS-PAGE analysis of the expression and purification steps of the Arthrobacter sp. 32c β-D-galactosidase expressed by E. coli host (A), P. pastoris GS115 pPICZαA-32cβ-gal methanol induced variant (B) and P. pastoris GS115 pGAPZαA-32cβ-gal constitutive variant (C). Lanes 1 – protein weight marker. Panel A: lane 2 – cell extract after expression, lane 3 – purified β-D-galactosidase after affinity chromatography. Panel B and C: lane 2 – broth after protein expression, lane 3 – protein precipitate, lane 4 – purified β-D-galactosidase after affinity chromatography.