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Utilization of Methionine by the Adult Rat

I. Distribution of the Alpha-Carbon of DL-Methionine-2-C¹⁴ in Tissues, Tissue Fractions, Expired Carbon Dioxide, Blood and Excreta¹

Departments of Home Economics and Chemistry, The Agricultural and Technical College of North Carolina, Greensboro, North Carolina

The appearance of the -carbon of methionine in 23 tissues and tissue fractions, globin, heme, excreta, and expired carbon dioxide of adult rats at various time intervals has been investigated.

The specific activity of bone marrow was higher than that of other tissues both at 4 and 24 hours. The activity of bone marrow protein, similarly, was higher than that of other tissues.

At 4 hours, the concentrations of radiocarbon in the water-soluble fractions of bone marrow, pancreas and adrenal glands were higher than those of other tissues; after 24 hours, in bone marrow, kidney, spleen and jejunum. The hexane fraction of 17 tissues contained radiocarbon.

The total concentration of radiocarbon in the water-soluble fraction decreased sharply over the 24-hour period, occurring concomitantly with an increase in the carbon fourteen content of tissue proteins.

The -carbon of methionine appeared in expired carbon dioxide within 15 minutes; in heme, in 7 minutes; and in globin, within 12 minutes. Incorporation of the -carbon of methionine into globin proceeded slowly, reaching a maximum at 24 hours.

When administered by stomach tube as a component of an adequate semi-synthetic diet, 17 mg of DL-methionine-2-C¹⁴ was absorbed during the 4-hour interval. Of the absorbed dose, 4.6% was eliminated as C¹⁴O₂ and 9.8% was present in tissues. At the end of 24 hours, 9% of the -carbon or methionine had been taken up by tissues, and 13% had been eliminated as C¹⁴O₂.

Manuscript received 22 June 1960.