Albany 2013: Book of Abstracts
June 11-15 2013
©Adenine Press (2012)
Isolation and partial characterization of a general hormone transporting blood protein complex
Using immobilized insulin, human blood serum insulin-binding proteins were isolated at physiological pH and zinc concentration. By means of enzyme-linked immunoassay, albumin (26.7 ± 1.75%), α- fetoprotein (2 ± 0.61%), transferin (10 ± 0.73%), retinol-binding protein (4 ± 0.75%) and immunoglobulin G (20.3 ± 0.95%) were identified in isolated protein complex from human blood serum.
Gel filtration of isolated proteins on Sephadex G-75 has demonstrated formation of a supramolecular complex under pH 7.2 and zinc concentration of 1 mg/ml (Garipova et al., 2010). The possible existence of such complex is supported by the presence of lipocalin glycoproteins such as retinol-binding protein and transferrin in obtained proteins; lipocalins form the protein family, which is capable to form intermolecular complexes to ensure the delivery of hormones to target cells through their own cell receptors (Flower et al., 1996).
It has been shown that the isolated protein complex, along with insulin, transports other hydrophilic hormones. By means of ELISA, protein hormones such as luteinizing (1 mU/mg) and thyreotropic (0.03 mM/mg) hormones, and prolactin (0.5 mU/mg) were identified. In addition, the complex has included hydrophobic hormones: thyroxin (11.0 ± 0.5 nmol /mg), triiodothyronine (1.3 ± 0.06 nmol/mg) and testosterone (7.0 ± 0.03 nmol /mg).
Based on these data, we have proposed an existence in human blood of a general transporting complex that is common for both hydrophobic and hydrophilic hormones. The core of this complex is formed by transporting proteins, including those relating to lipokalins. This complex transfers thyroxin, triiodothyronine, testosterone, thyroid-stimulating hormone, prolactin, luteinizing hormone, as well as triglycerides and cholesterol to the tissues.
The composition of insulin-binding protein complex was significantly changed in the insulin-dependent diabetes mellitus patient’s blood. Albumin and α-fetoprotein, which are present in a normal complex, are revealed only in trace amounts in samples isolated from the diabetic blood and are replaced by α 1-acid glycoprotein, and possibly other unidentified proteins.
Disturbance of hormone-transporting complex protein composition in the diabetic blood may be a reason of insulin delivery disruption. Perhaps for the same reason delivery to target cells of not only insulin, but also other members of the hormone–transporting complex are disrupted in the diabetic blood.
1, albumin; 2, α-fetoprotein; 3, transferin; 4, retinol-binding protein; 5, immunoglobulin G; 6, α1-acid glycoprotein; 7, unidentified proteins
Garipova M. I., Morugova T.V., Kireeva N.A., Ibragimov R.I., Pershina A.S., Eliseeva O.S. & Baranova M.V. (2010). Affinity extraction and study of insulin-binding protein of human serum. Problems of biological, medicinal and pharmaceutical chemistry. 8, 40-44.
Margarita I. Garipova
Bashkirian State University