Abstract
The ability of Bordetella heat-labile toxin (HLT) to induce ischemic lesions after intracutaneous injection to guinea pig skin was lost following incubation at 37°C with long-chain saturated acyl-CoA and acyl-carnitine compounds. Short-chain unsaturated acyl-CoA compounds, however, were less potent in inhibiting the induction of HLT activity. Long-chain saturated acyl-CoA and acyl-carnitine compounds, potently inhibited the induction of this activity. On incubation with HLT at 0°C, a long-chain saturated acyl-CoA compound, palmitoyl-CoA, did not inhibit HLT activity. When first mixed with bovine serum albumin or dimethyl-β-cyclodextrin, palmitoyl-CoA lost the ability to inhibit HLT activity. Binding of 14C-palmitoyl-CoA to HLT was measured by Scatchard analysis. The Bmax values of HLT (2.75 mol/mol of protein) were higher than that of acyl-CoA-binding protein from bovine liver (0.95 mol/mol of protein). Neither acyl-CoA hydrolase nor acyl-CoA ligase was detected in the HLT preparation. These results suggest that the acyl-CoA and acyl-carnitine compounds bind directly to HLT and produce a critical change in conformation required for HLT activity.
