ABSTRACT
Glutaminase was first discovered by H. A. Krebs in 1935 and he distinguished among a "brain type" and a "hepatic type" of the enzyme. The purification of Phosphate-activated glutaminase (PAG) from the pig brain is essentially similar, starting with an acetone powder extract. The molecular weight of rat kidney PAG is reported to be 160 kdaltons and this enzyme dimerizes and polymerizes similarly to pig kidney and brain PAG. The main activators of solubilized and purified renal and brain PAG appear to be phosphate and phosphorylated compounds such as riboflavin phosphate and trinucleotides. Other physiological inhibitors of PAG are the reaction products glutamate and ammonia. However, it should be noted that mouse brain astrocyte PAG is not inhibited by ammonia in contrast to neuronal PAG. The kinetics of PAG is very complex and purified pig kidney and brain PAG are allosteric enzymes.
