Identification of methionine as a possible precursor to the selenocysteine catalytic site of glutathione peroxidase

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1985

OSTI ID:6704262

Chung, C K

The selenium (Se) moiety of glutathione peroxidase (GSHPx) occurs as selenocysteine and is present at the catalytic active site of the enzyme which catalyzes the reduction of hydrogen peroxides and lipid peroxides. The presence of this unusual amino acid at the active site raises the question as to the origin of the carbon skeleton of Se-cysteine. ICR Swiss mice were fed a Se deficient diet for 50 days and then were fed a Se adequate diet (1 ppm Se as SeO/sub 3/). Mice were i.p. injected with either (U-/sup 14/C) methionine, serine, or alanine (0.5 ..mu..Ci/0.1 ml/mouse/day) for 25 days. Recovered GSHPx activity in liver and blood was carboxymethylated (CM) with iodoacetic acid. CM-GSHPx was partially purified by column chromatography. /sup 14/C-GSHPx fractions were collected, lyophilized, and hydrolyzed. /sup 14/C-amino acids were separated by TLC and ion-exchange chromatography. TLC (phenol, cyclohexane, acetic acid, and water (90;6.5;3.5;8)) revealed a GSHPx /sup 14/C-amino acid derived from U-/sup 14/C-methionine, but not from serine or alanine corresponding to CM-selenocysteine (R/sub f/; 0.16). Ion-exchange chromatography of U-/sup 14/C-methionine labeled GSHPx hydrolyzate revealed two radio carbon ninhydrin positive peaks corresponding to /sup 14/C-CM-selenocysteine and /sup 14/C-methionine. No corresponding /sup 14/C-labeled peaks were observed for CM-selenocysteine derived from U-/sup 14/C serine or alanine. The results suggest that methionine may contribute a portion of the carbon skeleton to selenocysteine which may include an alternative metabolic pathway. Animal studies demonstrated that GSHPx activity is increased by methionine supplementation may be due to its contribution of carbon source to the catalytic site of the enzyme.

• Research Organization: Texas Tech Univ., Lubbock (USA)
• OSTI ID: 6704262
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALANINES
AMINO ACIDS
ANIMALS
CARBON 14 COMPOUNDS
CARBOXYLIC ACIDS
CATALYSIS
CHEMICAL REACTIONS
CHROMATOGRAPHY
CYSTEINE
DRUGS
ELEMENTS
ENZYMES
GLUTATHIONE
HYDROXY ACIDS
ION EXCHANGE CHROMATOGRAPHY
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
LIPIDS
LIPOTROPIC FACTORS
LIQUID COLUMN CHROMATOGRAPHY
MAMMALS
METHIONINE
MICE
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXIDOREDUCTASES
OXYGEN COMPOUNDS
PEPTIDES
PEROXIDASES
PEROXIDES
POLYPEPTIDES
PROTEINS
RADIOPROTECTIVE SUBSTANCES
REDUCTION
RODENTS
SELENIUM
SEMIMETALS
SEPARATION PROCESSES
SERINE
THIN-LAYER CHROMATOGRAPHY
THIOLS
TRACER TECHNIQUES
VERTEBRATES