Aspergillus ficuum phytase activity is inhibited by cereal grain components

Abstract

In the current study, we report for the first time that grain components of barley, rice, wheat and maize can inhibit the activity of Aspergillus ficuum phytase. The phytase inhibition is dose dependent and varies significantly between cereal species, between cultivars of barley and cultivars of wheat and between Fusarium graminearum infected and non-infected wheat grains. The highest endpoint level of phytase activity inhibition was 90%, observed with grain protein extracts (GPE) from F. graminearum infected wheat. Wheat GPE from grains infected with F. graminearum inhibits phytase activity significantly more than GPE from non-infected grains. For four barley cultivars studied, the IC50 value ranged from 0.978 ± 0.271 to 3.616 ± 0.087 mg×ml-1. For two non-infected wheat cultivars investigated, the IC50 values were varying from 2.478 ± 0.114 to 3.038 ± 0.097 mg×ml-1. The maize and rice cultivars tested gaveIC50 values on 0.983 ± 0.205 and 1.972 ± 0.019 mg×ml-1, respectively. After purifying the inhibitor from barley grains via Superdex G200, an approximately 30–35 kDa protein was identified. No clear trend for the mechanism of inhibition could be identified via Michaelis-Menten kinetics and Lineweaver-Burk plots. However, testing of the purified phytase inhibitor together with the A. ficuum phytase and the specific protease inhibitors pepstatin A, E64, EDTA and PMSF revealed that pepstatin A repealed the phytase inhibition. This indicates that the observed inhibition of A. ficuum phytase by cereal grain extracts is caused by protease activity of the aspartic proteinase type.

Characteristics of the First Protein Tyrosine Phosphatase with Phytase Activity from a Soil Metagenome

“…It has been previously demonstrated that the phosphatase activity of soil-derived enzymes might be inhibited in the presence of aluminum hydroxides [40]. Moreover, Cu 2+ and Fe 2+ have been reported as strong inhibitors of several phosphatases and phytases from different organisms, such as S. ruminantium or Klebsiella terrigena [41,42]. These proteins were also strongly inhibited in the presence of Zn 2+ , which only has a minor effect on the activity of Pho16B.…”

Overexpression of Nepenthesin HvNEP-1 in Barley Endosperm Reduces Fusarium Head Blight and Mycotoxin Accumulation

“…Recently, we reported that barley crude protein extracts inactivate microbial phytases via aspartic acid proteinase activity, rather than through classical enzyme inhibition [35]. Activity inhibition-based purification and MS analysis of inhibitory fractions identified HvNEP-1 as a potent inhibitor of fungal phytases [36].…”

Globoids and Phytase: The Mineral Storage and Release System in Seeds

“…There are no known reversible proteinaceous inhibitors of phytases. Instead, plants appear to rely on proteases, e.g., to counter pathogen-secreted phytases [ 92 ]. This suggests that the activity of PAPhy_a is tightly controlled by the chemical environment, likely the pH, and/or localization.…”