4.1 Enzymatic factors.
Researchers found that during the protein harvest operation, high
mechanical shear force could cause cell lysis. Consequently, more
intracellular enzymes are released to the Harvest Cell Culture Fluid
(HCCF) thus lead to a higher level of disulfide bond reduction (Hutterer
et al., 2013; Trexler-Schmidt et al., 2010). Alternatively, low
dissolved oxygen (DO) levels in cell culture or HCCF can also cause
disulfide bond reduction since there is a limited amount of oxygen
molecules to consume NADPH, thus leaving enough NADPH as “electron
fuel” for the disulfide bond reduction reaction (Mun et al., 2015;
O’Mara et al., 2019). These aspects of root causes have been the focus
of recent industrial studies.