The effect of nordihydroguaiaretic acid and related lignans on formyltetrahydrofolate synthetase and carboxylesterase

Abstract

The lignans nordihydroguaiaretic acid (NDGA), heminordihydroguaiaretic acid (HNDGA) and norisoguaiacin were found to inhibit formyltetrahydrofolate synthetase (formate:tetrahydrofolate ligase (ADP-forming), EC 6.3.4.3) and carboxylesterase (carboxylic-ester hydrolase, EC 3.1.1.1) activity from a wide variety of sources. In all cases, NDGA was the most effective inhibitor. Synthetase activity was reduced by half at NDGA concentrations between 0.11 and 0.24 mM. Esterase activity consisted of NDGA-sensitive and NDGA-resistant forms. The sensitive class was half-inhibited by 2–4 μM NDGA. Irreversible inhibition of formyltetrahydrofolate synthetase by NDGA was observed both at low protein concentration (< 0.2 mg/ml) and at high protein concentration where precipitation of protein was observed. Inhibition of formyltetrahydrofolate synthetase by NDGA arises from a decrease in V max and increase in K m for all substrates. In contrast, NDGA affects only the V max parameter of the esterase activity. It is suggested that the broad range of enzymes inhibited by NDGA may be a consequence of the amphipathic character of the molecule and the flexibility to accommodate to a variety of binding sites. It is also suggested that the previously reported ability of NDGA to inhibit phagocytosis may be due to the compound's ability to inhibit carboxylesterases.