Susceptibility of mammalian deoxyribonucleases I (DNases I) to proteolysis by proteases and its relationships to tissue distribution: biochemical and molecular analysis of equine DNase I.

This research looks into the properties and function of deoxyribonuclease I (DNase I) in horses, comparing it to other mammalian DNase I. The study finds that the enzyme’s resistance or sensitivity to being broken down by other enzymes correlates to its tissue distribution.

Equine DNase I Purification and Analysis

• The researchers purified equine DNase I, an enzyme which breaks down DNA, from the parotid gland – a salivary gland in horses. They also cloned the cDNA (complementary DNA, which is synthesized from a messenger RNA template) corresponding to the enzyme.
• It was discovered that the mature form of this enzyme consists of 260 amino acids.
• In terms of enzymatic properties and structural aspects, the horse DNase I was found to be very similar to the DNase I of other mammals.

Classification of Mammalian DNase I

• DNase I enzymes in mammals have been categorized into three types depending on their tissue distribution: pancreatic, parotid and pancreatic-parotid. The horse DNase I showed the highest activity in the parotid gland and was classified as parotid-type.

Comparing Mammalian DNase I Susceptibility to Proteolysis

• The study compared how the different types of mammalian DNase I are affected by proteolysis, which is the breakdown of proteins by enzymes known as proteases.
• It was found that pancreatic-type DNase I was resistant to proteolysis by certain enzymes, namely trypsin and chymotrypsin, while parotid-type DNase I was not.
• Conversely, pancreatic-parotid-type DNase I was resistant to proteolysis by another enzyme, pepsin, whereas the other types were not

Mutagenesis Analysis and Molecular Evolution

• Experiments using site-directed mutagenesis, a method for creating specific gene mutations, showed that altering just a single amino acid did not change the enzyme’s resistance or susceptibility to proteolysis. The conclusion drawn was that over the course of molecular evolution, multiple changes contributed to these properties of mammalian DNase I.
• The enzyme’s ability to maintain activity in vivo, within the organism, is thought to have evolved in response to these properties.

In conclusion, the research sheds more light on the function and evolution of DNase I in mammals, a key enzyme involved in DNA metabolism.