these conditions, the enzyme activity did not change significantly when the lipase was stored for 6 months, and Lipase GH1 retained 50% of its initial activity (9000 U per mL) after storage for one year. No significant difference in enzyme activity was observed when the pH of the broth was adjusted from 5.0 to 10.0 and the broth was stored at 4 ◦C for 6 months. The situation was different for storage at 4 ◦C for 1.5 years. Under this condition, a lower culture supernatant pH was correlated with reduced Lipase GH1 stability; the enzyme activity was reduced by 50% for storage at pH 10.0 but was reduced by 72% (to 5000 U per mL) for storage at pH 5.0.
Degradation caused by pH-mediated destabilization is highly dependent on the stability of the recombinant protein itself, which is usually increased by glycosylation and disulfide bond formation
[21]. Because Lipase GH1 is a glycosylated protein, we hypothesized
that glycosylation helps promote the enzyme stability. Serine and
aspartic proteases (both secreted by P. pastoris) are activated at
low pH values, and this fact may account for the pH dependence of
proteolytic activity [21].
Our findings indicate that Lipase GH1 should be stored under
alkaline conditions. The stability of this enzyme is greater under
alkaline than acidic conditions, providing a basis for long-term
preservation. In view of its high activity, stability, and broad pH
tolerance, Lipase GH1 has excellent potential for industrial appli-
cations.