Catalytic oxidation of dithiols by a semisynthetic enzyme
The semisynthetic enzyme flavopapain (1C), obtained from the alkylation of Cys-25 of papain with 8..cap alpha..-(bromo-acetyl)-10-methylsioalloxazine (1B), was found to be an effective catalysts for the oxidation of dithiols to disulfides. The k/sub 2//K/sub s/ values for the oxidation of d,l-dihydrolipoamide and d,l-dihydrolipoic acid determined from anaerobic single-reaction stopped-flow kinetics were 4400 and 3400 M/sup -1/s/sup -1/, respectively. These values were, respectively, 126 and 200 times larger than the second-order rate constants for oxidation of d,l-dihydrolipoamide and d,l-dihydrolipoic acid by the model flavin 8-acetyl-10-methylisoalloxazine (1A). Under aerobic turnover conditions using the synthetic dye MTT as an electron acceptor, the k/sub cat/ and K/sub m/ values for the oxidation of d,l-dihydrolipoamide by 1C were in approximate agreement with the k/sub 2/ and K/sub s/ values, indicating that the rate-limiting step of the catalytic cycle is substrate oxidation rather than oxidation of dihydroflavopapain. When compared with flavopapains 2C and 3C (obtained as above but by modification with 7..cap alpha..- and 6..cap alpha..-(bromoacetyl)-10-methylisoalloxazine (2B and 3B, respectively)), flavopapain 1C is the most efficient catalyst. The circular dichroic spectra of flavopapains 1C, 2C, and 3C were recorded, and the dissociation constants of the sulfite addition complexes of 1C and 2C were determined.
- Research Organization:
- Rockefeller Univ., New York, NY
- OSTI ID:
- 5658763
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 108:12, Issue 12
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
DIAPHORASE
CATALYTIC EFFECTS
OXIDATION
CATALYSIS
SULFIDES
CHEMICAL PREPARATION
THIOLS
CATALYSTS
CHEMICAL REACTION KINETICS
EXPERIMENTAL DATA
CHALCOGENIDES
CHEMICAL REACTIONS
DATA
ENZYMES
HETEROCYCLIC COMPOUNDS
INFORMATION
ISOALLOXAZINES
KINETICS
NUCLEOTIDE DEHYDROGENASES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXIDOREDUCTASES
REACTION KINETICS
SULFUR COMPOUNDS
SYNTHESIS
400301* - Organic Chemistry- Chemical & Physicochemical Properties- (-1987)