(a) The
thyroxine-binding proteins were investigated in 23 cases of untreated
thyrotoxicosis and 16 cases of untreated
hypothyroidism, employing reverse flow paper electrophoresis with the
glycine acetate system at pH 8.6 in the Durrum type cell.(b) In active
thyrotoxicosis, all sera exhibited diminished
thyroxine-binding
prealbumin (TBPA) capacities. however, 17 of the 23 sera also had diminished thryroxine-binding
alpha globulin (TBG) capacities, as well as markedly elevated free
thyroxine fractions. In contrast, six thyrotoxic sera had normal TBG capacities and normal or slightly elevated free
thyroxine fractions.(c) In
hypothyroidism, the TBPA capacities showed no consistent deviation from the normal range. 11 of the 16 sera had elevated TBG capacities as well as markedly diminished free
thyroxine fractions. In contrast, five hypothyroid sera had normal TBG capacities and normal or nearly normal free
thyroxine fractions.(d) In
thyrotoxicosis and
hypothyroidism, the inverse correlation between free
thyroxine fraction and TBG was much closer than that with TBPA. When diagnostic categories were considered separately, only TBG bore a significant inverse relation to the free
thyroxine fraction. It is therefore suggested that in
thyroid diseases TBG may sometimes play a more important role than TBPA in determining the free
thyroxine fraction.(e) The demonstrated variations in the
binding proteins were considered sufficient to explain the abnormalities of the free
thyroxine fractions in
thyroid disease.