Inhibition chloroacetamide

CHLOROACETAMIDE INHIBITION OF FATTY ACID SYNTHESIS IN THE GREEN ALGA SCENEDESMUS ACUTUS... 

Over a decade ago, work on the enzyme aldolase reductase elegantly demonstrated this point. The noncovalent inhibitor alrestatin was modified to contain various electrophiles a-chloroacetamide, a-bromoacetamide or a-iodoacetamide. Noncovalent interactions between inhibitors and protein would not have changed, but molecules behaved differently based on the electrophile the weakest showed reversible inhibition, whereas the iodoacetamide displayed almost complete irreversible inhibition.1401 These results are an important warning if a reaction is too facile, irreversible reactions can obscure true binding affinities. 

The chlorine atom of a-chloroacetamide herbicides is activated by the adjacent carbonyl group, so chlorine easily reacts with nucleophiles, and hence with thiol groups. The covalent bonds formed result in inhibition of protein synthesis and wilting of the plant (Jaworski, 1969). 

CDAA (N-N-diallyl-2-chloroacetamide) was reported to reduce mitosis in barley (Hordeum vulgare L.) roots nearly 90% after 96 h at 57 yM (38). Propachlor (2-chloro-N-isopropylacetanilide) totally inhibited mitosis in onion (Allium cepa L.) root tips after an 18 h treatment with 75 yM (3 ). At 20 yM cell division was reduced approximately 50% and cell enlargement was reduced 40% in oat coleoptiles (39). After 24 h, 100 yM ioxynil (4-hydroxy-3,5-diiodobenzonitrile) reduced the mitotic index in broad bean (Vicia faba L. ) and pea root tips ( ). Few herbicides that inhibit cell division have been studied in adequate detail to locate the site of the block. A notable exception is the herbicide chlorsulfuron (DPX 4189, 2-chloro-N- [(4-methoxy-6-methyl-l,3,5-triazin-2-yl)amino]carbonyl -benzenesulfonamide) ( ). Ray reported a 50% reduction in corn growth 3 h after treatment with 28 yM chlorsulfuron. Mitosis in broad bean root tips was significantly reduced by 2.8 yM, whereas in three different tests, cell enlargement was not influenced with concentrations of 28 yM. Thymidine incorporation into DNA was inhibited in corn root tips after a 1 h treatment with... 

Phytotoxic diloroacetamides provided a linear relationship between severe inhibition of growth and inhibition of the incorporation of [ CJoleic acid into VLCFAs in Scenedesmus acutus [7]. In higher plants, the incorporation of [ C] stearic acid or malonyl-CoA into VLCFAs was inhibited by diloroacetamides while the formation of fatty acids up to Cig was not influenced [8]. Acyl elongation with 20 0-CoA and 18 0-CoA primer substrates was inhibited by the active (S)-enantiomer of metolachlor but not by the (R)-isomer [1, 9). Inhibition of VLCFA formation was also observed in metazachlor-resistance mutant (Mz-1) cells of S. acutus [9]. Thus, the phytotoxic action of chloroacetamide herbicides is most likely by the inhibition of VLCFA synthesis. 

Table 35. Minimum Inhibition Concentrations (MIC) of MCA and Chloroacetamide (CA) at Different pH Values in Nutrient Agar...

Table 43 Minimum inhibition concentrations (MIC) of MCA and chloroacetamide (CA) at different pH values in nutrient agar...

In the presence of metazachlor, alachlor or dimethenamid (5 pM) fatty acid desaturation in S, acutus was strongly inhibited after 40 h. Under these conditions the relative amounts of polyunsaturated fatty acids decreased while palmitic and oleic acids accumulated (Table 1). In an in-vitro assay, desaturation of oleoyl-CoA by microsomes was also decreased by chloroacetamides, suggesting a direct influence of the herbicides on oleic acid desaturation, although 25 pM were necessary for a significant inhibition (Table 2). l C-oleic acid fed to the algae was rapidly incorporated into the lipids and further desaturated. It was also incorporated into a precipitate obtained after saponification of the cells or lipid extraction. Radioactivity in that fraction was dramatically reduced by metazachlor, a concentration between 10 nM and 100 nM was sufficient for a 50% inhibition [3]. This effect was correlated with... 

Chloroacetamides induce an accumulation of 18 1 in 5. acutus and inhibit 18 1 desaturation in vitro. Furthermore, they dramatically reduce the incorporation of 18 1 into a non-extractable fraction after lipid or fatty acid extraction. This inhibition is specific to 18 1, requires metabolically active cells, and does not occur in a metazachlor tolerant line [6]. Oleic acid metabolism could thus play a central role in the mode of action of chloroacetamides. The NEF is currently under further investigation and its analysis might lead to the primary target of the herbicides. 

Chloroacetamide herbicides are applied for the control of preemergence grass and some broadleaf weeds. Their mode of action, however, is not understood. It has been reported that lipid synthesis is one of the target sites although such an effect is not seen with all tissues inhibition of cuticular wax formation has also been found. ... 

---