Proteins and enzymes

25


Proteins and enzymes



Plasma proteins


The biochemistry laboratory routinely measures ‘total protein’ and ‘albumin’ concentrations, usually in a serum specimen, and reports the ‘globulin’ fraction as the difference between the first two results. Some proteins (e.g. immunoglobulins) are measured as classes, and immunochemical methods are available for measuring specific proteins and hormones. Enzymes are measured both by determining their activity and by immunochemical methods to assess their mass.




Albumin


Albumin is the major plasma protein and is synthesized and secreted by the liver. It has a biological half-life in plasma of about 20 days and it accounts for about 50% of the total hepatic protein production. Albumin makes the biggest contribution to the plasma oncotic pressure. If the albumin concentration falls very low, oedema is the result (Fig 25.1). There are four main reasons for the occurrence of a low plasma albumin concentration:




Although serum albumin measurements have previously been used to monitor a patient’s response to long-term nutritional support, they are unreliable and insensitive.



Specific proteins


Measurement of a number of specific proteins gives useful information in the diagnosis and management of disease (Table 25.1). Characteristic changes in the concentration of certain plasma proteins are seen following surgery or trauma, or during infection or tumour growth. The proteins involved are called acute phase reactants (pp. 110–111). These acute phase proteins may be used to monitor progress of the condition or its treatment.



Table 25.1


Specific proteins that are measured in serum














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Jun 18, 2016 | Posted by in BIOCHEMISTRY | Comments Off on Proteins and enzymes

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Protein name Function Reason for assay
α1-antitrypsin Protease inhibitor Reduced in α1-antitrypsin deficiency
β2-microglobulin A subunit of the HLA antigen