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Dr.Kats posted an update
Free-form L-tryptophan
The nature of the stimulation of the growth of Streptococcus
lactis by yeast extract
https://sci-hub.ru/https://www.cambridge.org/core/journals/journal-of-dairy-research/article/abs/the-nature-of-the-stimulation-of-the-growth-of-streptococcus-lactis-by-yeast-extract/4414332BD10C85A1EB243326EBCE9A32#:~:text=https%3A//doi.org,a%20new%20window%5D
aevum2 Comments-
Fraction 3 = huge quantity of total amino acids and peptides (all sorts of building blocks). It gives ~75% of the stimulation.
Fraction 6 = tiny mass, mostly tryptophan, not a mix. It alone gives ~20% of the stimulation.
That means a single amino acid (free tryptophan), in microgram-scale availability, is contributing almost a THIRD of the total growth effect that you get from the entire amino-acid buffet of fraction 3.
That’s disproportionate.
If all amino acids were interchangeable “protein fuel,” then giving a huge pool of glutamate/alanine/aspartate/etc. (fraction 3) should fully solve growth. You wouldn’t expect adding a trace pool of mostly tryptophan (fraction 6) to matter that much.
But it does.
That tells you biologically:
Tryptophan was specifically limiting for continued high-rate growth of Streptococcus lactis C10 in milk.
Not “amino acids in general.” Not “nitrogen in general.” Specifically: bioavailable, immediately assimilable tryptophan. -
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