Mj. Hubbard et A. Carne, DIFFERENTIAL FEEDING-RELATED REGULATION OF UBIQUITIN AND CALBINDIN(9KDA) IN RAT DUODENUM, Biochimica et biophysica acta (G). General subjects, 1200(2), 1994, pp. 191-196
Analyses of the calcium-binding protein, calbindin(9kDa), purified to
apparent homogeneity (SDS-PAGE) from rat duodenum, revealed variable c
ontamination by two other 9 kDa proteins (up to 0.2 mol equivalent eac
h) which were identified as ubiquitin and its C-terminal variant, des-
Gly-Gly-ubiquitin. We found that the co-purification of these proteins
did not reflect a tight molecular interaction but instead their unexp
ectedly similar physical characteristics in nondenaturing conditions.
Like calbindin(9kDa), free ubiquitin was abundant (1% and 0.4% of solu
ble protein, respectively) in duodenum mucosa of 7-8-week-old rats and
its concentration varied daily and with feeding status. In rats fed f
rom midnight to 8.30 a.m., the ubiquitin concentration was specificall
y higher at 10 pm than at 10 a.m. (11.2 +/- 0.7 and 7.7 +/- 0.8 nmol p
er g wet weight, respectively, P < 0.02), whereas calbindin(9kDa) tend
ed towards an opposite variation (18.0 +/- 1.9 and 21.8 +/- 1.7 nmol p
er g, respectively). Based on its unusually high abundance and novel f
eeding-related variations, ubiquitin must have an important functional
role in the rat duodenum which is distinctly regulated from the calci
um transport-associated role of calbindin(9kDa).