The activation of chick liver tyrosine transaminase in vitro

The tyrosine aminotransferase mechanism

“…In six experiments the Km ± standard error of the mean for pyridoxamine phosphate was found to be 1.2 ± 0.1 X 10-6 m which agrees very well with the Km value of about 0.7 X 10-6 m for pyridoxal phosphate in this reaction (Kenney, 1959; Diamondstone and Litwack, 1963;Jacoby and LaDu, 1964). The tyrosine aminotransferase from chicken liver also appears to be activated by pyridoxamine phosphate (Constantsas and Knox, 1967) and the rat liver enzyme is protected from urea inhibition by pyridoxamine phosphate as well as by pyridoxal phosphate (Litwack etal., 1966). Figure 2 depicts an experiment to test whether pyridoxamine phosphate would activate isotopic exchange between tyrosine-U-14C and µ-hydroxyphenylpyruvate in the absence of a-ketoglutarate.…”