DIFFERENCES IN TRYPTOPHAN BINDING TO HEPATIC NUCLEI OF NZBWF(1) AND SWISS MICE - INSIGHT INTO MECHANISM OF TRYPTOPHANS EFFECTS

We have observed that in NZBWF(1) mice the affinity for L-tryptophan b inding to hepatic nuclei in vitro is markedly less than that of Swiss mice, In vitro binding of [H-3]tryptophan to hepatic nuclei from both strains was determined without and with unlabeled L-tryptophan(10(-4) mol/L). The relative specific binding of L-tryptophan to hepatic nucle i in vitro was 60.9 +/- 4.4% for Swiss mice and 35.8 +/- 5.4% (P < 0.0 1) in NZBWF(1) mice, The total specific binding (bound radioactivity/m g nuclear protein) of L-tryptophan to hepatic nuclei in vitro was 74.9 % (P < 0.05) lower in NZBWF(1) 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 he patic tryptophan dioxygenase activity in mice that were food-deprived overnight or 1 h after tube-feeding L-tryptophan (20 mg/100 g body wei ght) were similar in the strains of mice, in vitro [C-14] leucine inco rporation into protein using hepatic microsomes of mice 1 h after tube -feeding L-tryptophan (20 mg/100 g body weight) revealed a significant ly greater (P < 0.05) increase relative to food-deprived controls in S wiss mice (76.8 +/- 19.2%) than the increase in NZBWF(1) mice (26.5 +/ - 2.6%). Nuclear [C-14]-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 NZBWF, mice. Liver nuclear poly(A)-polymerase and n ucleoside triphosphatase activities were variably increased by the adm inistration of L-tryptophan in both strains. in summary, compared with Swiss mice, NZBWF, 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.