Inorganic cations and polyamines moderate pectinesterase activity

Inorganic and organic cations influenced pectinesterase (PE) activity and solubilization from Marsh grapefruit pulp. Activity increased to 281%, 183%, and 130% with lead acetate (6.8 mM), ferric chloride (0.2 mM), and calcium chloride (20 mM), respectively. The polyamines, putrescine, spermidine, and spermine had negligible stimulating effect. All cations tested inhibited PE activity at higher concentrations. Solubilization of total PE was decreased and thermostable PE (TS-PE) was not affected by polyamines. There was a progressive decline in total PE activity above 1.6 mM spermidine, 7.6 mM putrescine and 20.0 mM spermine. Loss of activity upon solubilization suggests that the TL-PE-pectate complex stabilized TL-PE. No change in TS-PE activity suggests that it may be bound with greater affinity, physically entrapped, or non-electrostatically bound.