Selenocysteine β-Iyaseの触媒機構

抄録

We have found that elemental selenium is released enzymatically from selenocysteine. The deuterium isotope effect at the αposition is about 2.4. This indicates that the αhydrogen of selenocysteine is removed by a base at the active site. When the enzyme is incubated with L-selenocysteine in the absence of added pyridoxal 5'-phosphate,the activity decreases with prolonged incubation time. However, the activity is recovered by addition of pyridoxal 5'-phosphate. The spectrophotometric studies show that the inactivated enzyme is the apo form. The apo enzyme is activated by a combination of pyridoxamine 5'-phosphate and various α- keto acids. This regulatory mechanism is analogous to those of aspartate β-decarboxylase, arginine racemase, and kynureninase.