a ligand of an mct protein or a nucleic acid encoding the mct and or ligand is also herewith provided regulation of the bioavailability of thyroid hormone in a tissue enables interfering with diseases the invention also provides pharmaceutical compositions comprising a compound capable of binding the mct protein or capable of influencing the binding or transporting of a ligand of the mct protein methods for diagnosis and or treatment of a disease such as a disorder of thyroid metabolism non thyroidal illness obesity or cardiovascular illness are also provided as well as bioassays for identifying or detecting a candidate drug capable of binding to or influencing at least part of the mct protein application_number US 99775704 A description the invention is further explained in the following examples the examples do not limit the scope of the invention they merely serve to exemplify the invention xenopus oocytes were isolated and injected with 4 6 ng rat mcts crna after 3 days groups of 10 injected or uninjected oocytes were incubated for 60 mm at 25 c with 10 nm radioactive iodothyronines in 0 1 ml medium uptake of iodothyronines was determined as previously described 18 the results are shown in fig1 transport of amino acids by mcts in oocytes xenopus oocytes were isolated and injected with crna coding for rat mct8 or with crnas coding for the heavy chain 4f2 and the light chain lat1 of the heterodimeric human l type amino acid transporter after 3 days groups of 10 injected or uninjected oocytes were incubated for 60 mm at 25 c with 10 u03bcm radioactive leu tyr trp or phe in 0 1 ml medium amino acid uptake was determined as previously described 18.