Properties of taurine : α-ketoglutarate aminotransferase of Achromobacter superficialis Inactivation and reactivation of enzyme

Abstract

The activity of taurine : α-ketoglutarate aminotransferase (taurine : 2-oxoglutarate aminotransferase, EC 2.6.1.55) from Achromobacter superficialis is significantly diminished by treatment of the enzyme with (NH 4) 2SO 4 in the course of purification, and recovered by incubation with pyridoxal phosphate at high temperatures such as 60°C. The inactive form of enzyme absorbing at 280 and 345 nm contains 3 mol of pyridoxal phosphate per mol. The activated enzyme contains additional 1 mol of pyridoxal phosphate with a maximum at 430 nm. This peak is shifted to about 400 nm as a shoulder by dialysis of the enzyme, but the activity is not influenced. The inactive form is regarded as a partially resolved form, i.e. a semiapoenzyme. the enzyme catalyses transamination of various ω-amino acids with α-ketoglutarate, which is the exclusive amino acceptor. Hypotaurine, dl-β-aminoisobutyrate, β-alanine and taurine are the preferred amino donors. The apparent Michaelis constants are as follows; taurine 12 mM, hypotaurine 16 mM, dl-β-aminoisobutyrate 11 mM, β-alanine 17 mM, α-ketoglutarate 11 mM and pyridoxal phosphate 5 μM.