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PubMed1985

Localization of the iron transport glycoprotein, uteroferrin, in the porcine endometrium and placenta by using immunocolloidal gold.

Uteroferrin, a glycoprotein implicated in transplacental iron transport in the pig, has been localized within the porcine uterus during mid pregnancy by using immunocolloidal gold labeling of sectioned material. In the endometrium where uteroferrin is synthesized, it was located exclusively in the non-ciliated cells of the glandular epithelium where it appeared to follow a common route of secretory glycoprotein from the cell (i.e., rough endoplasmic reticulum----Golgi----condensing vacuoles----secretory granules). Uteroferrin was present in the lumen of the glands and overlying placental areolae and in the large absorptive chorionic epithelial cells of the areolae. The latter cells contained numerous small vesicles and tubules as well as large endocytotic vacuoles. All these structures contained uteroferrin and are probably involved in translocating the glycoprotein in intact form from the uterine lumen to the blood capillaries draining the placenta.

Acid Phosphatase↗

PubMedDate not supplied

Possible function of carbohydrate on glycoproteins secreted by the pig uterus during pregnancy.

Uteroferrin is a purple iron-containing acid phosphatase secreted by the porcine uterus under the influence of the hormone, progesterone. It is synthesized by the glandular epithelial cells of the uterine endometrium and during pregnancy is taken up by specialized structures (areolae) opposite each uterine gland. Uteroferrin is then released into the fetal circulation and cleared by the liver or fetal kidney. A major role in iron transport to the fetus has been proposed. Uteroferrin, as purified from uterine secretions of pigs, possesses mainly high mannose (predominantly Man5 and Man6) chains. These oligosaccharide chains of uteroferrin appear to be responsible for its binding and uptake by reticuloendothelial cells of the fetal liver which is the major site of erythropoiesis of the fetus. Uteroferrin, although implicated in transplantal iron transport, also possesses many of the properties of a lysosomal enzyme and, when newly synthesized, carries the so-called lysosomal recognition marker, mannose 6-phosphate. The phosphate group is masked by a covering N-acetylglucosamine residue, a feature which may account for its secretion rather than retention within lysosomes. Evidence is also presented that the oligosaccharide chains of newly synthesized uteroferrin are larger than those of the mature form and are trimmed after secretion. The phosphate group is also removed. It is not clear whether uteroferrin carbohydrate is implicated in the movement of the glycoprotein across the placenta as well as its uptake by the fetal liver.

Acid Phosphatase↗