Density labelling studies of the photocontrol of L-phenylalanine ammonia-lyase in discs of potato (Solanum tuberosum) tuber parenchyme.

The photocontrol of L-phenylalanine ammonia-lyase (EC 4.3.1.5) activity in discs of potato (Solanum tuberosum) tuber parenchyme has been investigated by density labelling with 2H from 2H2O. Labelling of enzyme was measured by analysis of the equilibrium distribution of enzyme activity in CsCl density gradients as a function of buoyant density corrected with respect to the distribution of the external marker enzyme beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23). It is demonstrated that the white-light mediated stimulation of phenylalanine ammonia-lyase activity involves stimulation of the rate of de novo production of active enzyme.