on. This conclusion is further strengthened by the results when the WT BF1 was preincubated with MgADP. In the absence of the subunit, Chrysontemin preincubation with MgADP suppressed the ATPase activity of 33 proportionally at 12060783 a 33: MgADP ratio of 1:2, suggesting that binding of MgADP is strong and binding of one or two MgADP is enough to induce MgADP inhibition of 33 complex. In contrast, greater than 60% of the activity was retained in the presence of 1:2 MgADP and the subunit, indicating that binding of MgADP to 33 was highly suppressed by the subunit. This agrees well with our previous observation that the subunit of TF1 significantly suppresses the binding of MgADP. LDAO did not activate the extended-fixed 33S3C133C complex of BF1, indicating that the extended-state subunit reduced MgADP inhibition. Considering all of these results, we conclude that inhibition is not due to the stabilization of MgADP inhibition, but due to an essentially different and counteracting mechanism. We believe, therefore, that these properties must be common among various F1-ATPases, despite the differences in the mechanisms of inhibition. It should be noted, however, the subunit did not protect mutant 33S3C133C complex from MgADP inhibition by the preincubation with ADP. These apparent contradictory results may be due to the different catalytic site affinity for nucleotides between WT and the mutant 33 complexes, and/or different mode of the action of MgADP during preincubation and ATPase turnover etc. Further experiments, for example, measurement of nucleotide binding to the catalytic sites with WT and mutant 33 with and without subunit will give us a clue to resolve the differences between WT and the mutant in the MgADP preincubation experiment. Significance of regulation by the subunit and MgADP inhibition in vivo The results presented here indicate that the ATPase activity of BF1 is very low under normal conditions due to strong MgADP inhibition. Because B. subtilis lives in an aerobic environment and its ATP synthase is primarily used to synthesize ATP but not to hydrolyze ATP, as is the case for bacteria 17053790 such as E. coli that can grow anaerobically. The subunit may not act as an inhibitor of the ATPase activity of B. subtilis ATP synthase. In contrast, its ability to attenuate MgADP inhibition may be its primary role in the regulatory system. Experiments using B. subtilis with mutant FoF1 to address these questions are underway in our laboratory. Elucidation of the balance and the interplay of these two regulatory systems in different bacteria may be required to understand the regulation of bacterial ATP synthases. Sertoli cells are essential in spermatogenesis. It is well established that the number of SC conditions the efficiency of spermatogenesis as one SC can only support a limited number of germ cells. SC number is defined during the foetal and prepubertal periods. The SC proliferation arrest mainly depends on thyroid hormone T3. In rodents, during the post natal period, the arrest of SC proliferation and entry into differentiation is correlated with a peak of T3 blood level. Neonatal hypothyroidism in mice and rats leads to an increase in the weight of adult testis and epididymis due to an increase in the daily sperm production. For a while, it was assumed that thyroid hormone acts exclusively through nuclear receptors: TRa1, TRa2, TRb1, TRb2 encoded by the THRA and THRB genes. Among T3 receptors, TRa1 is ubiquitous and it was previously described that