Table 1.

Physiological benefits of compartmentalization of β-lactam biosynthetic enzymes

Physiological mechanisms.	Examples of benefitial effects
Sequestration of toxic intermediates or final products	Detoxification of phenylacetic or phenoxyacetic acid by transport into peroxisomes
Channeling of precursors or substrates for β-lactams biosynthesis away from primary metabolism	Storage of α-aminoadipic acid in vacuoles, away from the lysine biosynthetic pathway
Sequestration of intermediates for the temporal sequential formation of intermediates to final products	Temporal conversion of isopenicillin N into benzylpenicillin
Metabolic coupling of biosynthetic reactions and transfer of intermediates between co-localized enzymes	Putative coupling of ACVS and IPNS in the cytosol. Coupling of Phenylacetyl-CoA ligase and IPN acyl transferase Coupling of fatty acids catabolic and modifying enzymes
Localization in organelles having optimal pH or physiological conditions for the biosynthetic enzymes	IAT optimal activity at the pH values at peroxisomes Preservation of the thiol (-SH group) of the tripeptide under reduced redox conditions at the cytosol
Co-localization of enzymes in the membrane, or near the membrane of organelles for joint inclusion in transport vesicles for secretion	Protein assembly that includes VP16 and other proteins of the recognition/teethering membrane complex
Accumulation in vacuoles of proteins and intermediates to be degraded and recycled for biosynthesis of other metabolites	Colocalization of proteases and hydrolases in the vacuoles for recycling cellular materials
Formation of protein secretion complexes	Complexes facilitating secretion of secondary metabolites