Content and turnover of rat intestinal microvillus membrane aminopeptidase. Effect of methylprednisolone.

The reasons for the difference in aminopeptidase activity between jejunum and ileum and the changes in enzyme activity after corticosteroid administration were investigated in rat small intestine. The aminopeptidase activity of microvillus membrane in jejunum was higher than in ileum. Methylprednisolone treatment enhanced the enzyme activity in both regions. The amount of enzyme as measured by a competitive radioimmunoassay was higher in jejunum than in ileum, and methylprednisolone administration increased the content of aminopeptidase in both regions. The kinetic parameters of aminopeptidase from both regions showed no difference and were not affected by methylprednisolone treatment. The maximum incorporation of [3H]glucosamine into immunoprecipitable aminopeptidase in jejunum was greater than in ileum, and methylprednisolone administration increased the incorporation in both regions. The degradation rate of aminopeptidase in jejunum was higher than in ileum, and methylprednisolone administration had no effect on the rate of degradation in either region. It was concluded that jejunum has a greater content of aminopeptidase than ileum due to a higher rate of enzyme synthesis, and that methylprednisolone administration increases the enzyme content by increasing the synthetic rate.