1. What this paper actually found

Hutchings et al. describe the norit eluate factor as:

• Acidic in nature

• Containing an amino group

• Destroyed by strong acid

• Stable to alkali

• Found in vitamin-free casein but destroyed if casein is completely hydrolyzed

• Molecular weight ≈ 500

• Phosphorus not required for its biological activity

• Stimulates lactic acid bacteria like L. casei and S. lactis, but not L. arabinosus (which can synthesize it)

So this factor:

• is an amino acid–like molecule (acidic + amino group),

• heat and acid labile,

• integral to protein (released only upon digestion),

• biologically required by lactic acid bacteria that can’t synthesize it,

• and not a nucleotide, contrary to earlier claims.

2. Why this matches free-form L-tryptophan

Each biochemical property listed above aligns with L-tryptophan, not with folate or niacin:

Property of “norit eluate factor”

Property of L-tryptophan

Match

Acidic and contains an amino group

α-amino acid, amphoteric

Acid-labile, alkali-stable

Tryptophan destroyed by hot acid, more stable in mild alkali

Insoluble in most organic solvents

Tryptophan poorly soluble except in polar solvents

Not precipitated by basic reagents

Neutral–acidic amino acid, non-basic

Found in casein, destroyed by hydrolysis

Bound tryptophan liberated upon digestion, degraded if hydrolyzed too long

Not a nucleotide

Matches — tryptophan is not phosphorus-containing

Biological requirement for L. casei, S. lactis

Both species require tryptophan or niacin precursors

Thus, the “norit eluate factor” is chemically and biologically consistent with free-form L-tryptophan, not folate or a nucleotide.

The apparent folic acid activity later seen by microbiological assay was a misclassification—because L. casei and S. lactis both respond strongly to free tryptophan as well as folate coenzymes.

3. How this leads into Krehl’s 1944–45 studies

Krehl’s group explicitly used “the procedure of Hutchings et al., except that it was carried only through the norit eluate stage.”
That means:

• Their “norit eluate” from beef liver was the same factor characterized here.

• When they assayed it with L. arabinosus, which can syHutchinsniacin from tryptophan, they observed “nicotinic acid activity.”

• Therefore, the 56 µg/mL “nicotinic acid” they reported is actually 56 µg/mL of free L-tryptophan, behaving identically to nicotinic acid biologically.

4. Summary conclusion

The norit eluate factor described by Hutchings, Bohonos, and Peterson (1941) = free-form L-tryptophan, not folic acid, nucleotide, or biopterin compound.

ATTACHED:
GROWTH FACTORS FOR BACTERIA
XIII. PURIFICATION AND PROPERTIES OF AN ELUATE FACTOR
REQUIRED BY CERTAIN LACTIC ACID BACTERIA*
(Received for publication, August 16, 1941)