Comparison of histidine decarboxylases from rat stomach and brain with that from whole bodies of rat fetus.

Histidine decarboxylases from the stomach and brain of adult rats were purified 380- and 160-fold, respectively, and their properties compared with those of the enzyme from whole bodies of fetal rats (7600-fold purification). The molecular weights (about 90,000) and the apparent Km values for L-histidine (3 X 10(-4) M) of the three enzymes were similar. The pI value of the fetal enzyme was 5.0, and that of the brain enzyme was 5.4. Histidine decarboxylase of the stomach showed two peaks of activity corresponding to those of the fetal and brain enzymes (pI's of 5.0 and 5.4) on isoelectric focusing. Anti-fetal-histidine decarboxylase antiserum inhibited the stomach and fetal enzymes extensively, but the brain enzyme only slightly. These results indicate that there are at least two types of histidine decarboxylase in rat tissue.