The Journal of Nutrition Vol. 127 No. 2 February 1997, pp. 270-275
Copyright ©1997 by the American Society for Nutritional Sciences

Differences in Tryptophan Binding to Hepatic Nuclei of NZBWF₁ and Swiss Mice: Insight into Mechanism of Tryptophan's Effects

Manuscript received 6 May 1996. Initial reviews completed 18 June 1996. Revision accepted 28 October 1996.

George Washington University Medical Center, Department of Pathology, Washington, DC 20037

We have observed that in NZBWF₁ mice the affinity for L-tryptophan binding to hepatic nuclei in vitro is markedly less than that of Swiss mice. In vitro binding of [³H]tryptophan to hepatic nuclei from both strains was determined without and with unlabeled L-tryptophan(10⁴ mol/L). The relative specific binding of L-tryptophan to hepatic nuclei in vitro was 60.9 ± 4.4% for Swiss mice and 35.8 ± 5.4% (P < 0.01) in NZBWF₁ mice. The total specific binding (bound radioactivity/mg nuclear protein) of L-tryptophan to hepatic nuclei in vitro was 74.9% (P < 0.05) lower in NZBWF₁ mice than in Swiss mice. Other strains (DBA, SJL and BALB/c) had specific binding affinities similar to that of Swiss mice. Serum and hepatic free tryptophan concentrations and hepatic tryptophan dioxygenase activity in mice that were food-deprived overnight or 1 h after tube-feeding L-tryptophan (20 mg/100 g body weight) were similar in the strains of mice. In vitro [¹⁴C] leucine incorporation into protein using hepatic microsomes of mice 1 h after tube-feeding L-tryptophan (20 mg/100 g body weight) revealed a significantly greater (P < 0.05) increase relative to food-deprived controls in Swiss mice (76.8 ± 19.2%) than the increase in NZBWF₁ mice (26.5 ± 2.6%). Nuclear [¹⁴C]-labeled RNA release in vitro was increased 77.2 ± 18.0% by tube-feeding of L-tryptophan in Swiss but only 7.6 ± 5.8% (P < 0.02) in NZBWF₁ mice. Liver nuclear poly(A)-polymerase and nucleoside triphosphatase activities were variably increased by the administration of L-tryptophan in both strains. In summary, compared with Swiss mice, NZBWF₁ mice have a lower specific binding affinity for L-tryptophan by hepatic nuclei, and this alteration may account for the other differences in responses to L-tryptophan by the two strains.

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