Liberation, purification, and properties of thioesterase component of pigeon liver fatty acid synthetase complex

Inhibition of pigeon liver fatty acid synthetase by specific modification of lysine residues with 2,4,6-trinitrobenzenesulphonic acid

Pigeon liver fatty acid synthetase was inactivated irreversibly by 2,4,6-trinitrobenzenesulphonic acid (TNBS). Biphasic inactivation of the enzyme was observed with the inhibitor. NADPH provided protection to the enzyme against inactivation by TNBS and the extent of protection increased with NADPH concentration indicating that the essential lysine residues are present at the NADPH binding site. The stoichiometric results with TNBS showed that 4 mol of lysine residues are modified per mole of fatty acid synthetase upon complete inactivation. The rapid reaction of two amino groups per enzyme molecule led to the loss of 60% of the enzyme activity. These approaches suggested that two lysine residues present at the active site are essential for the enzymatic activity of fatty acid synthetase.

Evidence for the essential histidine at the NADPH binding site of enoyl-CoA reductase domain of pigeon liver fatty acid synthetase

Pigeon liver fatty acid synthetase was inactivated by stoichiometric concentrations of diethylpyrocarbonate (DEP). The second order rate constant for the loss of synthetase activity was similar to the value for enoyl-CoA reductase indicating that ethoxyformylation destroys the ability of the enzyme to reduce the unsaturated acyl intermediate, without significant effect on beta-ketoacyl reductase activity. NADPH provided protection to the enzyme against inactivation by DEP indicating that essential histidine residues are present at the active site. DEP-modified enzyme showed a characteristic absorption maxima at 240 nm confirming the formation of ethoxyformic histidine. The reversal of inactivation by hydroxylamine and a pKa value of 7.0 obtained from the pH-rate profile for inactivation again confirmed the specificity of DEP for histidine. Stoichiometric results showed that two moles of histidine residue per mole of enzyme are essential for the activity of FAS.

Amino acid sequence around the reactive serine residue of the thioesterase domain of rabbit fatty acid synthase

Two thermolytic peptides containing the reactive serine residue of the thioesterase domain of rabbit fatty acid synthase have been isolated and sequenched by Edman degradation and fast atom bombardment mass spectrometry. The sequence (V-A-G-Y-S-Y-G) contains the motif G-X-S-X-G found around the reactive serine residue of all known serine proteinases and esterases.

Solubilization, purification and kinetic properties of three membrane-bound long-chain acyl-coenzyme-A thioesterases from microsomes of photosynthetic tissue

Microsomal membranes of developing pea (Pisum sativum) leaves contained almost one third of the total long-chain acyl-CoA thioesterase activity found in the leaf cell. Three distinct forms of long-chain acyl-CoA thioesterase were purified by a combination of cholate-solubilization, dialysis, ion-exchange, and gel-filtration chromatography. Purification factors of 4600, 100 and 280 were achieved for the thioesterase forms I, II and III, respectively. Apparent molecular masses were: form I, 28 kDa; form II, 140 kDa; form III, 139 kDa. All the three thioesterases showed overlapping specificities towards palmitoyl-CoA, stearoyl-CoA, and oleoyl-CoA but were inactive towards short-chain acyl-CoAs, such as acetyl-CoA and malonyl-CoA. Each thioesterase exhibited complex kinetic behavior, which was consistent with differential affinities of the enzymes for monomeric and micellar forms of their substrates. The significance of the kinetic behavior and possible regulatory role of these enzymes are discussed.