Catalytic properties and conformation of hydrophobized alpha-chymotrypsin incorporated into a bilayer lipid membrane

A set of artificially hydrophobized alpha-chymotrypsin derivatives, carryin g 2-11 stearoyl residues per enzyme molecule, were synthesized and their ca talytic parameters and conformation in water solution and in the liposome-h ound state were investigated. Hydrophobization of alpha-chymotrypsin and it s further incorporation into phosphatidylcholine (PC) liposomes have no eff ect on the rate constant of the N-acetyl-L-tyrosine ethyl ester (ATEE) este r bond hydrolysis (k(cat)). At the same time, an increase in the number of stearoyl residues attached to the enzyme results in a drastic decrease of A TEE binding to the active center (K-M increase). Incorporation of the hydro phobized enzyme into the PC liposome membrane results in K-M recovery to ne arly that of native alpha-chymotrypsin. The above changes are accompanied b y partial unfolding of the enzyme molecules observed by fluorescence measur ements, The obtained results are of interest to mimic the contribution of s urface hydrophobic sites in the functioning of membrane proteins, (C) 1999 Federation of European Biochemical Societies.