Preparation of recombinant argininosuccinate synthetase and argininosuccinate lyase: expression of the enzymes in rat tissues.

Nitric oxide (NO) is synthesized from arginine by nitric oxide synthase, generating citrulline as another product, which can be recycled to arginine by argininosuccinate synthetase and argininosuccinate lyase. Rat argininosuccinate synthetase was expressed in Escherichia coli as a fusion protein with maltose binding protein, cleaved from binding protein, and purified. The purified synthetase had no enzyme activity. Rat argininosuccinate lyase was expressed in E. coli using pET-3a as a vector, and purified. The purified enzyme had a specific enzyme activity of arginine formation of 2.6 mumol/min/mg protein at 37 degrees C, the value being somewhat lower than those of the enzyme purified from various tissues. Antibodies against these enzymes were produced in rabbits. Immunoblot analyses showed that the two enzymes are most abundant in the liver, followed by kidney and testis. Smaller amounts of the enzyme proteins were present in other tissues. RNA blot analysis showed that the argininosuccinate synthetase mRNA was most abundant in the liver and kidney, followed by testis and other tissues. On the other hand, argininosuccinate lyase mRNA was most abundant in the testis, followed by kidney and liver, and by other tissues. These results show that argininosuccinate synthetase and argininosuccinate lyase are expressed both tissue-specifically and ubiquitously, and that practically all tissues have activities to convert citrulline to arginine.