Versatility of oxazolidine spin labels--a model study with acyl-alpha-chymotrypsin

The p-nitrophenyl ester of N-oxyl-4',4'-dimethyl-3-oxazolidinebutyric acid was synthesized. The resonance spectrum of the acyl-alpha-chymotrypsin intermediate of this substrate was found to have more motional freedom at the enzyme active site as compared to the acyl-enzyme prepared from the p-nitrophenyl esters of 1-oxyl-2,2,5,5-tetramethyl-3-carboxypyrrolidine and 1-oxyl-2,2,6,6-tetramethyl-4-carboxy-1,2,5,6-tetrahydropyridine. The flexibility and the versatility of Keana's oxazolidine spin labels as covalent conformational probes is discussed.