Nucleoproteins are conjugated proteins containing nucleic acids and basic protein-like protamine’s or histones. In nucleoproteins there are salt-like combination between positively charged basic proteins and negatively charged nucleic acids.
Cytoplasm also contains ribonucleoprotein which is found particularly in ribosomes. All living cells contain nucleoproteins and some of the simplest systems, such as viruses, consist entirely of nucleoproteins.
Protamine’s:
1. These basic proteins have low molecular weight and these are found in association with DNA chiefly in fish sperms.
2. They produce large quantities of arginine and less amounts of neutral amino acids on hydrolysis.
3. Their isoelectric pH is around 12.
4. The polypeptide chains of protamine’s are wrapped around DNA molecules in such a way that the positively charged arginine form salt linkages with the phosphates of the nucleic acids.
5. The best examples are salmin (salmon sperm) and clupeine (herring sperm).
Histones:
1. They are more complex proteins than protamine’s.
2. They have larger molecular weights and exist in combination with DNA.
3. They produce a variety of amino acids on hydrolysis.
4. Nucleohistones mainly occur in animal sperms, birds, erythrocytes.
De-oxy-ribonucleoproteins:
1. They are viscous material which are insoluble in 0.15 M NaCl but soluble in 1M NaCl solution.
2. They have high molecular weights of 10 million to several hundred millions.
3. They are highly elongated and thread-like in shape.
Ribonucleoproteins:
1. They are present in cytoplasm of the cells and ribosomes.
2. They are composed of proteins and ribonucleic acids.
3. Ribosomes of E. coli consists entirely of ribonucleoproteins.
4. Ribosomes from mammalian and plant sources contain about 40-50 per cent RNA, the remainder being proteins.