Protein glycosilation

Vitamin K carboxylase is a transmembraneous protein in the lipid bilayer of the endoplasmatic reticulum (ER). It is highly glycosilated and its C-terminal is on the luminal side of the membrane. Besides its function as carboxylase it takes part as an epoxidase in the vitamin K cycle (Fig. 1). For the binding of the y-carboxylase the vitamin K-dependent proteins have highly conserved special recognition sites. Most vitamin K-dependent proteins are carboxy-lated in the liver and in osteoblasts, but also other tissues might be involved, e.g., muscles. 

The class II secreted fungal heme peroxidases include the LMPs LiP, MnP and VP [70]. All of these enzymes are extracellular and contain protoporphyrin IX (heme) as prosthetic group. They use H2O2 or organic hydroperoxides as electron accepting cosubstrates during the oxidation of diverse compounds. They are secreted as glycosilated, 35-38 kDa size proteins. 

J. Stahl-Zeng, V. Lange, R. Ossola, K. Eckhardt, W. Krek, R. Aebersold, and B. Domon, High sensitivity detection of plasma proteins by multiple reaction monitoring of /V-glycosiles, Mol. Cell. Proteomics, 6 (2007) 1809-1817. 

Isoelectric focussing allows the separation of zwitterionic analytes such as proteins or peptides according to their isoelectric point, pi (section 1.1.1.1). lEF is applied to the separation and purification of proteins, peptides and amino acids on an analytical as well as preparative scale. The pi of a protein depends on the sum of all charges, as well as the 3D structure and post translational modiflcations such as phosphorylation, glycosilation and changes in oxidation state. The pi is, thus, a valuable parameter for studying post-translational modifications of proteins. 

Na" -K" -ATPase glycosylated P-subunit protein was identified in rat type II pneumocytes grown in primary cultures as a broad 50 kDa band when blotted with the polyclonal anti P, antibody SpET but could not be detected by blotting with other anti-P antibodies (Zhang et al. 1997). The lung P-subunit may be glycosilated differently from kidney and other tissues. 

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