title: Enzymes of vitamin B6 degradation. Purification and properties of 4- and 5-pyridoxolactonases.
abstract: 4-Pyridoxolactone and 5-pyridoxolactone, formed by dehydrogenation of pyridoxal or isopyridoxal during the bacterial degradation of vitamin B6 by Pseudomonas MA-1 and Arthrobacter Cr-7, respectively, are hydrolyzed to the corresponding acids by distinct inducible lactonases which were purified to homogeneity. 4-Pyridoxolactonase from Pseudomonas MA-1 has an Mr of 54,000 and contains two probably identical subunits of Mr = 28,600. It has a pH optimum of 7.0, a Km of 5.9 microM, and a Vmax at 25 degrees C of 35.2 mumol X min-1 X mg-1. 5-Pyridoxolactonase from Arthrobacter Cr-7 has an Mr of 65,200 and also contains two probably identical subunits of Mr = 32,800. It has a pH optimum of 7.1-7.7, a Km of 300 microM, and a Vmax at 25 degrees C of 21.5 mumol-1 X min-1 X mg-1. The two lactonases require no added cofactors or metal ions; their activities are inhibited by sulfhydryl reagents but are not affected by metal-chelating reagents. Although the two lactonases are entirely specific for their respective substrates, 4-pyridoxolactone is a competitive inhibitor (KI = 52 microM) for 5-pyridoxolactonase, and 5-pyridoxolactone is a competitive inhibitor (KI = 48 microM) for 4-pyridoxolactonase.
mesh_terms: D001173:Arthrobacter / Q000201:enzymology*; D002265:Carboxylic Ester Hydrolases / Q000302:isolation & purification* / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D011549:Pseudomonas / Q000201:enzymology*; D011736:Pyridoxine / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; C050712:4-pyridoxolactonase; C050711:5-pyridoxolactonase; D002265:Carboxylic Ester Hydrolases; D011736:Pyridoxine