Complex of. cap alpha. -chymotrypsin and N-acetyl-L-leucyl-L-phenylalanyl trifluoromethyl ketone: structural studies with NMR spectroscopy

Journal Article · Tue Dec 01 00:00:00 EST 1987 · Biochemistry; (United States)

OSTI ID:5301965

Liang, T C; Abeles, R H

A dipeptidyl trifluoromethyl ketone, N-acetyl-L-leucyl-L-(1-/sup 13/C)phenylalanyl trifluoromethyl ketone, was synthesized. This compound inhibits chymotrypsin with K/sub i/ = 1.2 ..mu..M. The complex formed between this inhibitor and ..gamma..-chymotrypsin was examined with /sup 1/H, /sup 13/C, and /sup 19/F NMR spectroscopy to establish its structure in solution. The keto group of the trifluoro ketone is present as an ionized hemiketal group as deduced from the comparison of its /sup 13/C chemical shift with those of model hemiketals. The pK/sub a/ of the hemiketal hydroxyl in the complex is approximately 4.9, which is about 4.2 units lower than the pK/sub a/ of model hemiketals. This observation provides direct evidence that serine proteases are able to stabilize the oxyanions of tetrahedral adducts. Evidence is also presented for the presence of an Asp-His H bond and protonation of the imidazole group of His-57 in the tetrahedral adduct. The pK/sub a/ of His-57 is higher than 10. This observation directly indicates that the pK/sub a/ of His-57 is elevated in a complex containing a tetrahedral adduct.

• Research Organization: Brandeis Univ., Waltham, MA
• OSTI ID: 5301965
• Journal Information: Biochemistry; (United States), Vol. 26:24
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
59 BASIC BIOLOGICAL SCIENCES
CHYMOTRYPSIN
BIOCHEMICAL REACTION KINETICS
CONFIGURATION INTERACTION
NUCLEAR MAGNETIC RESONANCE
ENZYME INHIBITORS
KETONES
BIOSYNTHESIS
CARBON 13
FLUORINE 19
HISTIDINE
NMR SPECTRA
PH VALUE
PROTONS
AMINO ACIDS
AZOLES
BARYONS
CARBON ISOTOPES
CARBOXYLIC ACIDS
ELEMENTARY PARTICLES
ENZYMES
EVEN-ODD NUCLEI
FERMIONS
FLUORINE ISOTOPES
HADRONS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROLASES
IMIDAZOLES
ISOTOPES
KINETICS
LIGHT NUCLEI
MAGNETIC RESONANCE
NUCLEI
NUCLEONS
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PEPTIDE HYDROLASES
REACTION KINETICS
RESONANCE
SERINE PROTEINASES
SPECTRA
STABLE ISOTOPES
SYNTHESIS
550601* - Medicine- Unsealed Radionuclides in Diagnostics
550201 - Biochemistry- Tracer Techniques