Acetolactate synthase (ALS) (ALS)

Acetolactate synthase (ALS), also known as acetohydroxyacid synthase (AHAS), is a key enzyme found in plants, bacteria, and fungi that catalyzes the first step in the biosynthesis of branched-chain amino acids (BCAAs), specifically valine, leucine, and isoleucine (McCourt & Duggleby, 2006). The enzyme functions as a multimer and requires thiamine pyrophosphate (TPP), flavin adenine dinucleotide (FAD), and a divalent metal ion for its catalytic activity (Duggleby & Pang, 2000). Because humans and other mammals lack the ALS enzyme and must obtain BCAAs through their diet, it serves as an ideal target for highly selective herbicides that exhibit low mammalian toxicity (Lonhienne et al., 2018). Several major classes of herbicides, including sulfonylureas and imidazolinones, exert their effect by binding to the ALS enzyme and blocking the synthesis of essential amino acids, which leads to the cessation of plant growth and eventual death (Garcia et al., 2017). Beyond its agricultural importance, ALS is being investigated as a potential therapeutic target for antimicrobial and antifungal drugs, as it is essential for the survival of various human pathogens (McCourt & Duggleby, 2006). However, the widespread use of ALS-inhibiting herbicides has led to the rapid evolution of resistance in many weed species, primarily through point mutations in the ALS gene (Garcia et al., 2017).

Other names

Acetohydroxyacid synthaseAHASEC 2.2.1.6

Inhibition of the enzyme blocks the synthesis of branched-chain amino acids (valine, leucine, and isoleucine), leading to metabolic starvation and cessation of growth (Lonhienne et al., 2018).