Biochemical and immunohistochemical analysis of an unusual rat brain agmatinase

Abstract

Agmatine plays neurotransmitter/neuromodulatory actions in the brain. It result from decarboxylation of arginine by arginine decarboxylase and it is hydrolysed by agmatinase. Recently, we have cloned an unusual rat brain protein with agmatinase activity, although their deduced sequences greatly differ from all known agmatinases. However, in spite of only 12% identity with E. coli agmatinase, the rat brain protein is recognized by a polyclonal antibody raised against the bacterial enzyme. Like E. coli agmatinase, the rat brain enzyme exhibits an absolute requirement for Mn2+, not related to a metal‐binding LIM domain detected in its sequence. As shown here, the Mn2+ requirement is retained by a variant lacking the domain. We, therefore, associate Mn2+ to the hydrolytic reaction in the enzyme active site. Also described here is the generation of a polyclonal antibody against the brain agmatinase, which also reacts with the E. coli enzyme. We conclude that, although not sequence‐related, the rat brain agmatinase is structurally related to all known agmatinases. By immunohistochemical analysis, the enzyme was detected in arquate nucleus, ciliated ependymal cells and tanycytes hypothalamic. Since this coincide with that for agmatine, the enzyme would play a central role in regulating the levels and thus, the neurotransmitter/neumoregulatory actions of the primary amine in the brain. Grant FONDECYT 11070069