Chymotrypsin inhibitory conformation of dipeptides constructed by side chain-side chain hydrophobic interactions.
A complete series of configurational isomers (L-L, L-D, D-L and D-D) of a dipeptide Leu-Phe benzyl ester have been synthesized and assayed for chymotrypsin. In the conformational analysis by 400 MHz 1H NMR, the L-D and D-L isomers, but not the L-L and D-D isomers, showed fairly large upfield shifts (0.2-0.4 ppm) of Leu-beta CH2 and gamma CH proton signals, indicating the presence of shielding effects from the benzene ring. In addition to distinct signal splitting of Phe-beta CH2, the NOE enhancement observed between Leu-delta CH3 and Phe-phenyl groups revealed that these groups are in close proximity. These data indicated that L-D and D-L isomers form a hydrophobic core between side chains of adjacent Leu and Phe residues. When the dipeptides were examined for inhibition of chymotrypsin using Ac-Tyr-OEt as a substrate, the L-L isomer showed no inhibition, itself becoming a substrate. However, the other three isomers inhibited chymotrypsin in a competitive manner, and the D-L isomer was strongest with Ki of 2.2 x 10(-5) M. It was found that the D-L isomer was only slowly hydrolysed but the L(or D)-D isomer was not. H-D-Phe-L-Leu-OBzl with the inverse sequence of H-D-Leu-L-Phe-OBzl inhibited chymotrypsin more strongly (Ki = 6.3 x 10(-6) M).(ABSTRACT TRUNCATED AT 250 WORDS)
Sakamoto
H
H
Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka, Japan.
Shimohigashi
Y
Y
Maeda
I
I
Nose
T
T
Nakashima
K
K
Nakamura
I
I
Ogawa
T
T
Kawano
K
K
Ohno
M
M
D002918:Chymotrypsin / Q000037:antagonists & inhibitors*; D004151:Dipeptides / Q000737:chemistry* / Q000494:pharmacology*; D007536:Isomerism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011487:Protein Conformation; D013329:Structure-Activity Relationship
D004151:Dipeptides; D002918:Chymotrypsin