ABSTRACT
Two forms of GABA transaminase which could be distinguished by ion-exchange chromatography have been separated and purified in pig brain. The two forms have different Km values for alpha-ketoglutarate and show different degrees of inhibition by various salts. Although the two forms are separable, they have identical antigenic properties, pH optima, and NH2 terminal amino acid composition, and they appear to be of the same molecular size. The biological significance or the relationship between multiple forms of GABA transaminase is not yet understood.
Subject(s)
4-Aminobutyrate Transaminase/isolation & purification , Brain/enzymology , Transaminases/isolation & purification , 4-Aminobutyrate Transaminase/metabolism , Amino Acids/analysis , Animals , Epitopes , Isoenzymes/isolation & purification , Isoenzymes/metabolism , Kinetics , Molecular Weight , SwineABSTRACT
Cyclic GMP was found in primary cultures of glial cells obtained by dissociation of newborn mouse brain hemispheres. Its basal level (0.52 pmoles/mg cell protein) was as high as that found in adult mouse brain cortex but 10 times lower than in cerebellum. When glia were grown in the presence of dBcAMP, astrocytes changed their morphology; cGMP level increased and reached about 8 to 10 times the basal value. This increase was dose dependant with cAMP and was enhanced by the presence of 5mM Theophylline. Two hypothesis are discussed, either a direct action oc cAMP on glial cGMP metabolism or an indirect one on the protein activator of cGMP phosphodiesterase.
Subject(s)
Cyclic GMP/metabolism , Neuroglia/analysis , Animals , Bucladesine/pharmacology , Cells, Cultured , Mice , Neuroglia/drug effectsABSTRACT
4-Aminobutyrate-transaminase (4-aminobutyrate: 2-oxoglutarate amino-transferase, EC 2.6.1.19) from pig liver has been purified to electrophoretic homogeneity. It has a molecular weight of about 110 000 and is composed of two subunits of the same molecular weight but of different charges. Two forms of pig liver 4-aminobutyrate-transaminase were isolated by DEAE-cellulose chromatography and designated as 4-aminobutyrate-transaminase I and 4-aminobutyrate-transaminase II, corresponding to a cationic and anionic form. Some physical and kinetic properties of liver enzyme were compared to those of brain enzyme and no significant difference were found, except for their sedimentation coefficients and the charges of their subunits. The role of 4-aminobutyrate-transaminase in liver remains a matter of speculation, but could be related to a metabolic function.
