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The fate of tryptophan in the isolated perfused rat liver was investigated. It was shown that the liver removed the L-isomer more rapidly from the perfusate than the D-isomer. The 10 g liver was capable of a removal rate of 35 mg/hour when 42 mg of DL-tryptophan was given initially, followed by infusion at the rate of 42 mg/hour. Carbon-14 from DL-tryptophan-2-14C appeared in CO2much more rapidly and to a greater extent within 3 hours than did that from DL-tryptophan-7a-14C. In contrast to whole-animal studies, it was shown that overloading doses of acetoacetate were labeled by DL-tryptophan-5- or 7a-14C. The labeling pattern in acetoacetate was similar to that observed when 14C-fatty acids are the substrate. Acetoacetate overloading suppressed the production of radioactive carbon dioxide from DL-tryptophan-7a-14C.

SL- and DL-allo-5-hydroxylysine-6-14C and L-5-hydroxlysine-3H were administered intraperitoneally to intact rats and the degradative products were trapped by the metabolite overloading technique. Hydroxylysine was readily oxidized; approximately 40% of the 14C was expired as 14CO2in 24 hours. Urinary 5- hydroxypipecolate, α-ketoadipate, glutarate and crotonate were identified as labeled degradation products isolated from the urine. The specific activities of glutamate, aspartate and alanine isolated from the carcass protein were too low to permit the determination of the labeling pattern. This low activity and the rapid release of 14CO2suggests that C(6)of hydroxylysine reaches these amino acids via 14CO2. The degradation of hydroxylysine appears to proceed by reactions parallel to those which degrade lysine with the site of dehydroxylation as yet uncertain.