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Methylmalonate, Formiminoglutamate and Aminoimidazolecarboxamide Excretion of Vitamin B₁₂-deficient Germfree and Conventional Rats^1,2,3,

Department of Nutrition, University of California, Davis, California 95616

In order to evaluate the net influence of microbial metabolism on vitamin B₁₂ nutriture, growth and urinary methylmalonic acid (MMA), aminoimidazolecarboxamide (AIC) and formiminoglutamic acid (FIGLU) were measured in male germfree and conventional rats fed a low methionine diet with or without vitamin B₁₂ and during dietary supplementation with 1% of DL-methionine. Growth was retarded significantly among vitamin B₁₂-deficient rats of both environments in comparison with their respective vitamin B₁₂-supplemented controls. MMA excretion rose to 20 times the control level in conventional deficient rats but was only slightly elevated among germfree deficient animals. Though less dramatic, the same trend was true of AIC excretion. FIGLU excretion was elevated significantly in deficient animals of both environments. Methionine ingestion further enhanced MMA excretion of conventional deficient rats, suggesting that it served as a metabolic precursor. AIC excretion was unaffected by methionine feeding in contradiction to an earlier report. FIGLU excretion was depressed by DL-methionine supplementation to a greater extent among conventional than among germfree rats, perhaps indicating poor utilization of the D-isomer by germfree animals. These results show that MMA excretion is an unreliable index of vitamin B₁₂ deficiency in the absence of conventional microbial metabolism and that the vitamin B₁₂ requirement may be reduced in the germfree state.

KEY WORDS: • methylmalonate • formiminoglutamate • aminoimidazolecarboxamide • germfree • vitamin B₁₂

¹ This study contributed to Western Regional Research Project W-112 and was supported in part by Regional Research Fund 2594 and in part by grant no. 417 from the Nutrition Foundation, Inc.

² Portions of these data were taken from a thesis submitted by Jane M. Abbott in partial fulfillment of the requirements for the M.S. degree, University of California, Davis, June, 1971.

³ Portions of these data were presented at the annual meeting of the Federation of American Societies for Experimental Biology, Atlantic City, 1970 (Federation Proc. 29: 633 (abstr.).

Manuscript received 12 August 1971.