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Vitamin B2 activity of 7,8-dimethyl-10-(2,3,4-trihydroxy-4-formylbutyl)isoalloxazine in Lactobacillus casei.

The microbial activities of vitamin B2-aldehyde and vitamin B2-acid, produced by Schizophyllum commune, a Basidiomycete, were studied. Lactobacillus casei ATCC No. 7469 was used as a test microorganism. B2-aldehyde exhibited a good response curve in the growth of L. casei. B2-acid had neither a stimulatory nor an inhibitory effect on the growth. When B2-aldehyde was incubated with the homogenate of L. casei, it was converted to riboflavin. The flavin formed from B2-aldehyde by the homogenate not only exhibited an equivalent response curve to authentic riboflavin in the growth of L. casei, but also showed the same Rf value as authentic riboflavin in any paper chromatogram, as far as tested. Hence, the microbial activity of B2-aldehyde for L. casei seems to be ascribable to riboflavin which is a reduction product of B2-aldehyde.


Microbial activity of B2-acid
The B2-aldehyde preparation contained B2-acid as an impurity. The microbial activity of B2-acid for L. casei was studied and B2-acid was isolated and crystallized according to a previous paper (3,4). The result is shown in curve 3 of Fig. 1. Although the concentration of B2-acid was increased to 53.5ng/ml, growth was not  observed. The effect of adding B2-acid together with B2 was also tested. As shown in curve 4 of Fig. 1, the response of L, casei was dependent on the concentration only of B2; therefore, B2-acid did not seem to have any effect on the growth of L . casei. This result suggested that the observed activity of B2-aldehyde was not influenced by any contaminating B2-acid. 3 4. Microbial activity of the B2 produced from B2-aldehyde with the homogenate of L. casei Some isomers of B2 have been studied with respect to their biological activities. For example, it was reported that araboflavin had some activity for L. casei (9,10). We studied the microbial activity of B2 produced by the homogenate (the sample B2), comparing it with authentic B2 in order to obtain information as to whether the sample B2 was a true D-riboflavin. If the product from B2-aldehyde with the homogenate is D-riboflavin, its activity should be equivalent to that of B2.
The sample B2 in the homogenate reaction mixture was separated by PPC using ethyl acetate-pyridine-water as a developer and then was eluted from the paper with deionized water. The eluate was used as the sample B2 without further purification.
Authentic B2 was charged on the same filter paper, and treated by PPC in the same way as the sample B2 as described above, so that the influence of impurities during the preparation of the sample B2 might be compensated.
As shown in Fig. 4, the sample B2 showed the same response curve in the growth of L. casei as the authentic B2, D-riboflavin. Therefore, it is almost conclusive that the product from B2-aldehyde is D-riboflavin.
From the results of these studies it could be determined that B2-aldehyde possessed the stimulatory activity for growth of B2-requiring L. casei, and that the microbial activity of B2-aldehyde seems attributable to the normal metabolism of B2 which was produced by an enzymatic reduction of B2-aldehyde in L. casei.