Hypothetical model for regulation of prozyme translation.

Monomeric TbAdoMetDC has low activity and active enzyme is generated by heterodimerization with prozyme. The active complex catalyzes the decarboxylation of AdoMet to dcAdoMet. Upon stimuli, including knockdown or chemical inhibition of TbAdoMetDC, knockdown of TbAdoMetSyn, or methionine starvation, dcAdoMet pools decrease. This depletion signals upregulation of prozyme mRNA translation. Newly synthesized prozyme then complexes with inactive TbAdoMetDC monomers to form active heterodimers to compensate for the loss of flux in the decarboxylation of AdoMet. TbAdoMetDC protein suppresses prozyme mRNA translation when dcAdoMet levels are high. This repression is alleviated by low levels of dcAdoMet.