Calcitonin Activity of Particulate Fractions of the Ovine Thyroid Gland

Abstract

Mitochondria, nu dei, and microsomes obtained from ovine thyroid slices wh ich had been incubated in Krebs-Ringer bicarbonate buffer containing 4.8, 11.5 or 26.0 mg% concentration of calcium were assayed for calcitonin activity in rats. The microsomal preparatioa was the only particulate fraction to exhibit marked hypocalcemic activity and the hormonal activity of this fraction was enhanced by a 26.0 mg% calcium concentration in the incubation medium. The identity of the hypocalcemic species in the microsomal fraction with a calcitonin preparation 01' known potency was established by polyacrylamide gel eletrophoresis and by isoelectric focusing. The ovine microsomal calcitonin was resolved into two pro tein bands with isoelectric points (pl's) of 3.49 and 3.84. Both of these protein peaks exhibited hypocalcemic activity. The porcine standard calcitonin was resolved into two protein bands with pl's of 3.70 and 3.94.