Albumin and alkaline phosphatase as factors involved in the regulation of tyrosine phenol-lyase activity.

Holotyrosine phenol-lyase (EC 4.1.99.2), a pyridoxal-5'-phosphate (PLP)- requiring enzyme, was shown to rapidly dissociate when injected into BDF1 mice. The holoenzyme dissociated when incubated in plasma but not 0.01 M potassium phosphate (pH 7.4) buffer at 37 degrees C. A nonspecific alkaline phosphatase from calf intestine was found to inactivate the holoenzyme at pH 7.4 and 37 degrees C. This inactivation was inhibited in the presence of 0.5 M potassium phosphate buffer. Two other PLP-requiring enzymes, aspartate aminotransferase (EC 2.6.1.1), and alanine aminotransferase (EC 2.6.1.2) were inactivated by alkaline phosphatase in a similar manner. Incubation of holotyrosine phenol-lyase in the presence of bovine serum albumin also resulted in a reduction of holoenzyme activity but partially protected the enzyme from inactivation by alkaline phosphatase. A nuclear fraction having PLP-hydrolyzing activity also inactivated holotyrosine phenol-lyase. A regulatory function for alkaline phosphatase in the metabolism of PLP-requiring enzymes is suggested by these data.