Proteins in which amino acids and other components can be found on wet analysis are called conjugated proteins. A conjugated protein consists of two parts. Protein part and non-protein part. The protein part is called apoenzyme and the non-protein part is called prosthetic group. Conjugated proteins depending on the prosthetic group are:
1. Nucleoprotein: All the proteins that are made up of amino acids and nucleic acids are called nucleoproteins. All these proteins are located in chromosomes. It is soluble in water. These proteins are found in cell nuclei, viruses and ribosomes. For example, chromatin.
2. Glycoprotein: All the proteins that are made up of amino acids and sugars or glucose are called glycoproteins. If these proteins contain fructose instead of glucose, they are called mucoproteins and if they contain galactose, they are called galactoproteins. It is soluble in alkali. Cell membranes, jellyfish and saliva contain this protein. Eg- thyroglobin (thyroid), plasma glycoprotein (liver), immunoglobulin (blood cells), ribonuclease (RNA), deoxyribonuclease (DNA), mucin, peptidoglycan (bacteria), ovoalbumin (ovum).
3. Lipoprotein: The organic compound formed by the combination of protein and lipid is called lipoprotein. It is soluble in water, but insoluble in organic solvents. It forms the membranes of different types of cells. There are 5 types of lipoproteins. Chylomicrons, VLDL, LDL, IDL and HDL.
4. Phosphoprotein: All proteins that are formed by amino acids and phosphate or phosphorus are called phosphoproteins. It is insoluble in water, but soluble in organic solvents. E.g. Casein (Milk), Ovovitelin (Egg) etc.
5. Chromoprotein: Prosthetic group of proteins formed by dyes is called chromoprotein. Eg- Bilirubin, Chlorophyll, Hemoglobin, Carotenoids, Flavoprotein, Rhodopsin, Biliprotein, Myoglobin, Cytochrome, Hemocyanin etc.
6. Metalloprotein: The prosthetic group of protein which is formed by any metal (Fe, Mn, Mg, Zn, Cu, Co, Mo) is called metalloprotein. Such as siderophyllin, ceruloplasmin, ferridoxine, cytochrome, oxidase, ferritin, nitrogenase, hemoglobin etc.
7. Flavoprotein: The protein which is attached to flavin compound (FAD) is called flavoprotein. Eg- Sulfide reductase, succinate dehydrogenase, NADH-dehydrogenase etc.
8. Porphyrin: The protein that porphyrin is associated with iron or cytochrome is called porphyrin or cytochrome protein. E.g. Cytochrome-b.