Purification and Characterization of Triokinase from Porcine Kidney

Abstract

In order to be able to use triokinase for the enzymatic assay of tissue glyceraldehyde, we purified the enzyme to homogeneity from porcine kidney and characterized its biochemical properties. The purification was performed by polyethylene glycol fractionation, anion exchange chromatography, hydroxyapatite chromatography, hydrophobic chromatography, and gel filtration. The enzyme was purified 937-fold from the crude extract with an overall yield of 28 %. It had a molecular weight of 122,000 and was a dimer composed of identical subunits. The optimal pH and optimal temperature were 7.0 and 60 °C, respectively. This enzyme was stable when incubated at pH 7.0 at 40 °C for 1 h in the presence of 0.1 mg/ml bovine serum albumin. No loss of activity occurred for at least 1 month when the enzyme was stored at 4 °C in the presence of 1 mM dithiothreitol and 15 mM NaN₃ under N₂. Only three compounds, i.e., D-glyceraldehyde, dihydroxyacetone, and glycolaldehyde, acted as the substrate of the enzyme, having Km's of 11, <5, and 260 μM, respectively. The Km for ATP-Mg²⁺ was 68 μM. These results indicate that porcine kidney triokinase has properties advantageous for the glyceraldehyde assay using glyceraldehyde-3-phosphate dehydrogenase as a coupling enzyme.