Effect of cobalt and vitamin B¹² on the peroxidase and iodinating activity of mouse thyroid and submaxillary gland: in vitro stimulation of vitamin B¹² coenzyme on the iodination of tyrosine

Abstract

The peroxidase and iodinating activity of thyroid and submaxillary glands of mouse have been studied. The 105,000xg supernatant of mouse thyroid or submaxillary gland homogenate shows significant true peroxidase activity as indicated by guaiacol assay and by the estimation of pseudoperoxidase activity of contaminated hemoglobin. This peroxidase activity from thyroid or submaxillary gland enzyme preparation shows significant increase after intramuscular administration of cobalt or vitamin Bi2. Although 105,000×g supernatant of thyroid homogenate shows appreciable peroxidase activity, it does not incorporate iodine enzymatically to form monoiodotyrosine (MIT). The iodinating activity is located in the 8000×g and 105,000×g pellets, the latter showing higher specific activity. The 105,000×g pellet of mouse thyroid gland shows significant inhibition of MIT formation after cobalt administration while it shows significant stimulation of iodination after vitamin Bi2 treatment. The peroxidase activity of the same preparation does not appreciably change after cobalt or vitamin B12 treatment. The submaxillary gland 105,000×g supernatant fraction shows significant stimulation of iodination after cobalt or vitamin B12 injection. The enzyme preparation from normal mouse also shows increasing iodinating activity after in vitro addition of increasing doses of vitamin B12 coenzyme. Cobalt in vitro inhibits the iodinating enzyme of thyroid, while it has no appreciable effect on that of the submaxillary gland. Cobalt or vitamin B12 administration has no effect on the α-amylase activity of submaxillary gland and tyrosine transaminase activity of thyroid or submaxillary gland.