The three main substrates of fatty acid synthesis are malonyl-CoA, acetyl-CoA, and NADPH. During the process of fatty acid synthesis, the ATP-dependent carboxylation of acetyl-CoA to malonyl-CoA occurs via acetyl-CoA carboxylase 1 (ACC1). ACC1 is a biotin-dependent enzyme which is covalently bound to a lysyl residue of the carboxylase. The resulting malonyl-CoA generated is then converted via a multistep reaction to 16 carbon fatty acid palmitate through fatty acid synthase. Malonyl CoA is a crucial substrate as it functions to regulate fatty acid oxidation and inhibits the enzyme CPT1. This prevents fatty acids from going into the mitochondria for oxidation. Fatty acid synthase is a multicatalytic enzyme which depends on NADPH to fuel its functions. The process of fatty acid synthesis uses two molecules of NADPH for every molecule of acetate produced into the long-chain fatty acids.