Studies on the Time Cource of Free Amino Acid Concentration and of the Incorporation of C¹⁴-Threonine into Tissue Proteins of Rats fed on a Diet containing a Balanced Amino Acid Mixture (Part 2)

Incorporation of Orally Administrated C¹⁴-Threonine

Abstract

Rats were fed on a balanced amino acid diet which contained threonine-U-C¹⁴ as a tracer. At 24 hours after one meal feeding, distribution of ingested C¹⁴ in expired CO2, urine, muscle, intestinal tracts, liver, and plasma were about 40, 5, 20, 10, 5, and 2%, respectively. In liver and plasma, distribution of C¹⁴ in protein fraction was greater than that in free amino acid (FAA) fraction. In muscle, on the other hand, amount of C¹⁴ in protein fraction was the same as that in FAA fraction till 12 hours after feeding, and then the counts of C¹⁴ in FAA decreased, while that in protein continuously increased. Total maximum counts in organs were obtained at 12 hours after a meal, and the counts in muscle, intestine, and liver decreased afterward. The decrease of C¹⁴ in muscle and plasma was disapparence of FAA fraction and that in liver was due to decrease of both FAA and liver weight.
The amount of protein synthesized was calculated on the basis of some assumptions. During 12 hours, about 100 and 40mg protein were synthesized in muscle and liver, respectively, from dietary amino acids.