Update on the status of metrology for metalloproteins

Metalloproteins, which represent about 30% of the total proteome, are often important markers for distinguishing between healthy and diseased states of patients. As such markers have become increasingly important in clinical diagnostics, some of these proteins are routinely analysed in clinical laboratories. Reliable and comparable results are the basis for the investigation of changes in the proteome due to different health conditions. Nevertheless, for many proteins the results achieved with different routine measurement procedures or in different laboratories vary widely, thus hampering medical insights and the development of treatments. Reference measurement procedures with results traceable to the International System of Units (SI) will also help to greatly improve the performance of routine measurement procedures and, this way, they support the understanding of changes in the metallome. This perspective will give an overview of the efforts during the last three years to achieve reliable quantification of metalloproteins. The analytes covered were chosen due to their importance in clinical diagnostics. Haemoglobin (HGB), transferrin (TRF), superoxide dismutase (SOD) or ceruloplasmin (CER), for example, can serve as markers for diseases such as Down's syndrome in prenatal diagnostics (e.g. SOD), inflammation (acute-phase proteins such as TRF) or deficiency diseases (e.g. HGB, TRF, and CER). Moreover, they are used for the control of treatment efficiency, e.g. total HGB as the most important marker for anaemia treatment or the glycosylated form of haemoglobin A (HBA(1c)) for the treatment of diabetes. On the other hand, selenoproteins, namely glutathione peroxidase (GPX), seem to play an important role in cancer prevention and in reducing the side effects of chemotherapies.