Amino-4-Imidazolecarboxamide Ribotide Directly Inhibits Coenzyme A Biosynthesis in Salmonella enterica

Aminoimidazole carboxamide ribotide (AICAR) is a purine biosynthetic intermediate and a by-product of histidine biosynthe-sis. In bacteria, yeast, and humans, accumulation of AICAR has been shown to affect an array of cellular processes by both direct and indirect mechanisms. In purine biosynthesis, AICAR is the substrate of the bifunctional protein phosphoribosylaminoimi-dazolecarboxamide formyltransferase/IMP cyclohydrolase (PurH, EC 2.1.2.3/3.5.4.10). Strains lacking PurH accumulate AICAR and have a defect in the synthesis of the 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP)moiety of thiamine. The forma-tion of HMP is also compromised in vivo when coenzyme A (CoA) levels are reduced. Our results show that the in vivo accumu-lation of AICAR decreased total CoA pools and, further, that AICAR inhibited the activity of pantoate -alanine ligase in vitro (PanC, EC 6.3.2.1). These results demonstrated a mechanism of AICAR action and provide new insights into the metabolic con-sequences of disrupting purine metabolism. Historically, cellularmetabolismhas been described in the con-text of discrete metabolic units (e.g., biosynthetic or degra-dative pathways), a perspective that facilitated efforts to under-standmetabolic components such as enzymes andmetabolites. In reality, these units are integrated to form a complex metabolic network whose connectivity is mediated extensively by metabo-lites. Under appropriate circumstances (i.e., growth conditions o