Dietary regulation of aldolase isozyme expression in rat intestinal mucosa

Changes of aldolase A and B protein levels and their mRNA levels due to starvation for 48 h in mucosae of the jejunum, ileum, and colon were determined by Western and Northern blot analyses. In fed rats, B protein and B mRNA were predominant in the jejunum. In the ileum, both A protein and A mRNA, as much as B protein and B mRNA, were present in significant amounts. In the colon, A protein and A mRNA were predominant. The enzyme activity levels in those segments of fed rat intestine were in parallel to total enzyme protein levels (A + B) and also to total mRNA levels (A + B), thus suggesting that aldolase isozyme expression in fed rat intestine is determined mainly at the level of transcription. Starvation for 48 h caused about 30% reduction of both B protein level and B mRNA level in jejunum. In the ileum, both A and B mRNA levels were lowered 30-40% from those of fed rats, while A and B protein levels were reduced slightly (A, 0%; B, 12%). In the colon, starvation caused about 50% increase of A mRNA level and about 10% reduction of A protein level. By measuring the synthetic rate of the enzyme proteins from in vivo [35S]methionine incorporation, the accumulation of A mRNA in this tissue was suggested to be due to the significant fall of the translation rate of A mRNA. The translational and post-translational controls of aldolase isozyme expressions in rat intestines are discussed.