Ribonuclease deoxyribonuclease inhibition

The existence of a deoxyribonuclease in E. coli bound to an inhibitory RNA was first suggested by Kozloff (3< ) who found that the DNase activity of freshly prepared extracts could be markedly enhanced by pretreatment with ribonuclease. The enzyme was subsequently purified and freed of inhibitor (39). The purified enzyme termed endonuclease I could, in turn, be competitively inhibited by a variety of RNA s including transfer RNA, and Ri values as low as 10-8 M (nucleotide) have been observed (40). Examination of various purified RNA species and synthetic polyribonucleotides for their inhibitory activity has led... 

Some enzymes are rendered inactive by specific or unspecific inhibitors, as in the case of ribonuclease and deoxyribonuclease. Other enzymes have latent activity because their active center is in some way inactivated by some polypeptidic chain in the molecule. Once the inhibiting chain has been removed by the action of proteolytic enzymes, the enzyme becomes fully active, as is the case for example, for thrombin and chymotrypsin. Finally, the activity of some enzymes is kept latent because of the absence of a cofactor e.g., phenylpyruvic hydroxylase in the developing liver). 

The different procedures for isolating nucleic acids yield products which vary considerably in composition and properties. One reason for this is the presence of nucleolytic enzymes in most plant and animal tissues. Work is always carried out at as low a temperature as possible to retard this enzyme activity and sodium citrate is used in an attempt to inhibit the action of deoxyribonucleases ribonucleases are inactivated with guanidine hydrochloride or dodecylsulphate. 

Protein synthesis is inhibited by ribonuclease (cf. 376), whereas deoxyribonuclease generally, though not always, has little effect (379). 

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