Channelling of exogenous phenylalanine to the sites of storage and the sites of alkaloid and protein biosynthesis in Penicillium cyclopium.

Externally applied L-phenylalanine rapidly equilibrates with the cytosolic pool(s) in hyphae of emerged cultures of Penicillium cyclopium. If not incorporated into protein it is accumulated in the so called expandable pool, which is presumably localized in the vacuolar compartment. At high concentrations of exogenous L-phenylalanine practically all of the amino acid needed for protein synthesis comes from the extracellular source, contrary to alkaloid synthesis which under all conditions recruits more than 90% of the required L-phenylalanine from intracellular sources. Two pathways of alkaloid labelling can be distinguished, by which externally applied L-phenylalanine reaches the sites of alkaloid synthesis: (1) a direct way from cytosolic pool (primary labelling) and (2) an indirect way via the expandable pool (secondary labelling).