Development of Glutaminase Along the Villus–Crypt Axis in the Jejunum of Rat

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Abstract
The activity of glutaminase (E.C. 3.5.1.2), the entry enzyme for oxidation of glutamine, was measured in enterocytes isolated along the villus-crypt axis from rat jejunum. Specific activity of glutaminase was 5.05 .+-. 0.24 .mu.mol glutamate/mg protein/h in villus cells (fully differentiated cells) and 4.16 .+-. 0.30 in the deep crypt (undifferentiated cells). Activity of glutaminase was significant (p < 0.05) increased in cells isolated from the villus-crypt junction (differentiating cells) compared to the activity of the enzyme in both the villus and crypt at 6.21 .+-. 0.45. A similar pattern of activity of glutaminase was observed when the cells of the villus-crypt gradient were separated by sequential horizontal sectioning with a cryostat. Oxidation of L-[U-14C]glutamine to 14CO2 was also significantly (p < 0.01) higher in cells isolated from the villus-crypt junction compared to both villus or deep crypt cells. The quantity of glutaminase protein was determined by a dot immunobinding assay using an antibody to purified glutaminase. Immunoreactive glutaminase protein relative to total cellular protein was 6.06 .+-. 0.40 cpm/.mu.g homogenate protein in the villus cells, 3.01 .+-. 0.24 (p < 0.05) at the villus-crypt junction, and 4.49 .+-. 0.57 (p < 0.05) in the deep crypt. Thus, the highest activity of glutaminase present in the villus-crypt junction is the result of an increase in activity of the enzyme rather than an increase in the enzyme protein.