Species specificities of l-glutamic acid decarboxylase: Immunochemical comparisons

The relationship of catfish brain l-glutamic acid decarboxylase (GAD) with those from other species were examined by comparing the extent of their interactions with antibodies against catfish brain GAD. Several immunochemical methods, such as immunodiffusion, inhibition of enzyme activity and microcomplement fixation tests were employed for these studies. Antibodies against GAD from catfish brain were observed to cross-react with the enzymes from goldfish, frog, chick and turtle. Rabbit and bovine GAD did not cross-react with these antibodies. In the presence of the antibodies, enzymes from goldfish, frog. Drosophila, chick and crayfish were inhibited 27, 46, 32, 38 and 57% respectively. Enzymes from all the other species examined were not affected at all. Microcomplement fixation tests showed that goldfish, frog and chick GAD were quite similar in immunoreactivities. These immunochemical studies demonstrated that GAD from lower vertebrates such as chick, goldfish and frog and some invertebrates such as Drosophila and crayfish are closely related to catfish GAD. In contrast, mammalian GAD shows little or no cross-reactivity with antibodies against catfish GAD.