Human fetal testis endoplasmic reticulum glucose-6-phosphatase enzyme protein

Microsomal glucose-6-phosphatase (EC 3.1.3.9) is an enzyme system traditionally thought to be present only in gluconeogenic tissues. We have used microassay techniques, immunohistochemistry using monospecific antibodies to the liver enzyme, and specific DNA probes and primers to examine whether glucose-6-phosphatase is present in human and rat testis. Microsomal glucose-6-phosphatase activities in human fetal testis (weeks 15-20 of gestation) are approximately 25% of corresponding liver values. Localization is predominantly in Leydig cells, with variable and weak immunoreactivity in developing seminiferous tubules. Kinetic analysis of glucose-6-phosphatase in intact and disrupted microsomes and Southern blot analysis of polymerase chain reaction products indicated that the specific glucose-6-phosphatase enzyme system was also present in rat testis. We have shown for the first time that specific microsomal glucose-6-phosphatase activity, protein, and mRNA are present in testis, and that the predominant site of expression is the Leydig cell in human fetal testis.