The effect of herbicides (basagran, zenkor, kusagard, roundup, setoxidim, and lontrel and lontrel complexes with some doubly charged metal ions) and fungicides (tachigaren and tilt) on the activity of nicotinamide adenine dinucleotide (NADH) oxidoreductase from the methylotroph Methylococcus capsulatus (strain M) was studied. All the herbicides and fungi cides inhibit the enzyme, differing in the degree and type of inhibition. The inhibition con stants K i for these compounds and for lontrel complexes were determined. A correlation between the K i values and the complexation constants of these pesticides with NADH was established. The studied compounds are toxic.Quite a few data concerning the influence of herbi cides and fungicides on various components of the living cell, 1-3 in particular, on some enzymes, 4-11 have been reported. In our previous studies, 12-15 we demonstrated the formation of complexes of a number of pesticides with adenosine triphosphoric acid (ATP), nicotinamide ad enine dinucleotide (NADH), and nucleic acids. Despite the enormous scale of production and use of chemical means for cultivated plant protection, there is still no unified view on the mechanism of their action. Probably, each pesticide acts through its own mechanism.Nicotinamide adenine dinucleotide functions together with several vitally important enzymes. Therefore, it has been of interest to perform a kinetic study of some widely used pesticides on the activity of an enzyme acting to gether with NADH. As this enzyme, we chose NADH oxi doreductase (NADH OR, [EC 1.6.99.25]) from the methylotroph Methylococcus capsulatus (strain M), 16 which transfers electrons for mixed reduction of oxygen to wa ter, methane transformation to give methanol in the ac tive site of methane hydroxylase, and the reduction of dioxygen to water in the active site of cytochrome oxidase. The enzyme studied consists of four subunits, each in cluding FAD and an iron sulfur cluster, 2Fe-2S; 17,18 NADH OR functions according to the following scheme:where A is acceptor. The sequence of electron transfer from NADH to an electron acceptor is still unknown. However, by analogy with other reductases, one can suggest that the electrons are transferred from NADH to FAD and then to the iron sulfur 2Fe-2S cluster and to the electron acceptor. Neotetrazolium chloride (NT) was used in this work as the artificial electron acceptor.Enzymes of this type are present in the cells of almost all organisms. Therefore, the general features of the inter action of this enzyme with pesticides can also be applied to NADH OR from other organisms.Here we present data on the kinetics of NADH OR inhibition by commercial herbicides and fungicides of various structures and several complexes of the herbicide lontrel with doubly charged metal ions.
ExperimentalReagents. Commercial NADH (nicotinamide adenine di nucleotide) and NT (Sigma No. 2251, Reanal, Hungary) were used. The active substances of the herbicides and fungicides (their formulas are shown below) were isolated from commer cia...
