and Associationof the Enzymewith PyridoxalPhosphate

with tris(hydroxymethyl)aminomethaneor six other buffers. Pyridoxal phosphate at an incubation concentration of 130 imol/lfter reactivated the entire apoenzyme portion of an apoenzyme/holoenzyme mixture within 5 mm in tris(hydroxymethyl)aminomethane; in contrast, less than 20% was associated during 15 mm in phosphate. Activity measured in tris(hydroxymethyl)aminomethanebuffer without exogenous pyridoxal phosphate was 4% greater than that in phosphate and was slightly increased by Increasing the pH of the assay mixture from 7.5 to 8.0. Aspartate in the incubation medium did not retard the stimulationin tris(hydroxymethyl)aminomethane buffer.Whilethemagnitudeofstimulation var