Marker enzymes are cell biomarkers, which are not ubiquitous but confined to and produced by specific type of cell organelles and these are used to recognize and differentiate the specific organelle from complex cellular compartments.
The well-organized eukaryotic organisms, such as animals and plants, are composed of millions of cells. Under microscope, they may appear different from others. Even though, each cell of whole organism’s body derived from a single fertilized cell during development and contain a complete set of chromosomes similar to other cells of that body.
Genetically, all cells are same but functionally they are developed in different types of tissues, such as skin, muscle, nerves, and blood. These specialized tissues express only specific subsets of the total genome resulting into activating specialized genetic pathways and leaving others biological functions inactive.
If we jump into cytoplasm of the cell, the same set of organelles present in every cell of the body irrespective of their location and function. These cellular organelles present in specialized areas within a cell and involved in the various types of metabolic functions.
The development and organization of these internal cellular compartments (organelles) in proper range and position within the cell allow cells to successful differentiation of tissues, organs, and body plans.
In laboratories, a generalized analogy such as using the marker enzymes as experimental tools to separate the particular organelle from others. Using this marker enzymes, scientists are screening the various types of abnormities within the cell.
Marker enzymes of different organelles and their function
Marker enzymes are those enzymes which are confines to specific organelle, they help in differentiating that organelle from others.
Different organelles have different marker enzymes, such as-
- Cytosol and its marker enzyme: Cytosol is intracellular fluid and also known as cytoplasmic matrix made up of water and some inorganic and organic compounds dissolved in it such as soluble ions and proteins. It also contains insoluble suspended particles like ribosomes, which play role in protein translation. Cytosol contain some marker proteins like Lactate dehydrogenase (LDH).
- Plasma membrane: 5′-nucleotidase
- Endoplasmic Reticulum: Neutral alpha-glucosidase, alpha glucosidase
- Golgi Bodies: Galactosyl Transferase
- Lysosomes: N-acetyl-beta glucosaminidase
- Mitochondria: Malate dehydrogenase,
- Mitochondria (inner membrane): ATP Synthase
- Mitochondria (outer membrane): Monoamine oxidase
- Mitochondria (matrix): Citrate Synthase
- Nucleus: LaminA and Lamin C
- Perioxisomes: Catalase
If we take the human lymphocytes to characterize its cellular organelles, first we should lyse the cell membrane with erythrocyte hypotonic lysis buffer. Further, the obtained homogenates of mixed lymphocytes have to subject to analytical sub-cellular fractionation using sucrose gradient centrifugation. The centrifugation process separates the cellular compartments in different gradients based on their weight and density in the buffer. According to their density we can separate the layer of particular organelles from centrifuged tube and finally we can characterize them using marker enzymes or proteins.
- Shah T, Webster AD, Peters TJ. Enzyme analysis and subcellular fractionation of human peripheral blood lymphocytes with special reference to the localization of putative plasma membrane enzymes.Cell Biochem Funct. 1983 Jul;1(2):117-24.