In situ structural analysis of microsomal UDP-glucuronyltransferases by radiation inactivation

Journal Article · Sat Apr 15 00:00:00 EDT 1989 · J. Biol. Chem.; (United States)

OSTI ID:6149476

Vessey, D A; Kempner, E S

The structure of the UDP-glucuronyltransferases in microsomes from guinea pig and rat liver was examined in situ by radiation inactivation analysis. The p-nitrophenol conjugating activity of guinea pig microsomes increased at lower doses of radiation; at higher doses (greater than or equal to 36 megarads), activity showed a first order decline yielding a target size of 71 +/- 9 kDa. Treating microsomes with Triton X-100 eliminated the activation seen at lower doses of radiation and yielded a simple exponential decrease in activity which gave a larger target size (95 +/- 18 kDa). A monoexponential decrease in activity was seen in sonicated microsomes, at greater than or equal to 36 megarads. The same response was obtained when the reaction was assayed in the reverse direction. The estrone conjugating activity of guinea pig microsomes was similarly activated at lower doses of radiation and declined at higher doses (greater than or equal to 36 megarads), with a target size of 57 +/- 11 kDa. Allosteric activation of the enzyme by UDP-N-acetylglucosamine was eliminated by lower doses of radiation. Thus, activation of the enzyme by radiation, detergent, sonication, and UDP-N-acetylglucosamine appear to be interdependent. These activations are postulated to be due to the existence of the enzyme in an oligomeric form which can be dissociated into monomers with higher activity. The same biphasic activation-inactivation curves were obtained for p-nitrophenol conjugation in rat liver microsomes. The target sizes were 54 +/- 8 kDa (p-nitrophenol in the forward direction) and 66 +/- 10 kDa (p-nitrophenol in the reverse direction). Thus, the enzyme appears to be smaller in rat liver as compared with guinea pig liver. Lithocholate glucuronidating activity in rat liver microsomes (at greater than 36 megarads) gave a target size of 74 +/- 1 kDa.

• Research Organization: Veterans Administration Medical Center, San Francisco, CA (USA)
• OSTI ID: 6149476
• Journal Information: J. Biol. Chem.; (United States), Vol. 264:11
• Country of Publication: United States
• Language: English

Related Subjects

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
NITROPHENOL
BIOLOGICAL EFFECTS
TRANSFERASES
MOLECULAR STRUCTURE
BIOLOGICAL RADIATION EFFECTS
ENZYME ACTIVITY
ESTRONE
GLUCOSAMINE
GUINEA PIGS
IN VITRO
LIVER
MICROSOMES
AMINES
ANIMALS
AROMATICS
BODY
CARBOHYDRATES
CELL CONSTITUENTS
DIGESTIVE SYSTEM
ENZYMES
ESTRANES
ESTROGENS
GLANDS
HEXOSAMINES
HEXOSES
HORMONES
HYDROXY COMPOUNDS
KETONES
MAMMALS
MONOSACCHARIDES
NITRO COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANOIDS
ORGANS
PHENOLS
RADIATION EFFECTS
RODENTS
SACCHARIDES
STEROID HORMONES
STEROIDS
VERTEBRATES
560120* - Radiation Effects on Biochemicals
Cells
& Tissue Culture
560300 - Chemicals Metabolism & Toxicology