Abstract
The known diminution in penicillin formation by added lysine is thought to occur via feedback regulation of the lysine biosynthetic pathway, thus depleting the cells of α-aminoadipic acid, a precursor of penicillin. Studies were conducted to determine whether feedback repression or inhibition is the key mechanism involved. Lysine at 20 mM prevented net penicillin formation by starved mycelia of Penicillium chrysogenum Wis. Q-176 and Wis. 54-1255 until the extracellular lysine concentration fell by 90%. Growth in lysine did not reduce incorporation of L-valine-U-14C into penicillin by washed suspensions of either strain. On the other hand, the presence of lysine in the suspension system did lower valine incorporation. The data show that lysine acts by inhibition of enzyme action rather than by repression of enzyme synthesis.
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