Sex difference in L-glutamine D-fructose-6-phosphate aminotransferase activity of mouse submandibular gland.

L-Glutamine D-fructose-6-phosphate aminotransferase (2-amino-2-deoxy-D-glucose-6-phosphate ketol-isomerase (amino-transferring), EC 5.3.1.19) activities in the three main salivary glands of male and female mice were measured. It was found that the activity in the submandibular gland was about 10 times more in females than in males, whereas the activities in the sublingual and parotid glands of males and females were similar. The activity in the submandibular gland of female mice was not affected appreciably by ovariectomy but it decreased to the level in males on injection of testosterone. The activity in males was not affected appreciably by injection of progesterone or 17beta-estradiol, but it increased to the level in females after castration. The increased activity in castrated male mice was decreased again to the normal level by testosterone injection. Thus, this sex difference is caused by androgen, not by female hormones. On the basis of in vivo experiments using actinomycin D, it was suggested that testosterone produced an "enzyme inhibitor", which suppressed the enzyme activity in the submandibular glands of androgen-rich animals.