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The primary structure of muskrat pancreatic ribonuclease
Abstract:
Pancreatic ribonuclease from muskrat (Ondatra zibethica) was isolated and its amino acid sequence was determined from tryptic digests of the performic acid-oxidized and the reduced and aminoethylated enzyme. The peptides have been positioned in the sequence by homology with other ribonucleases. This could be done unambiguously for all peptides except Arg-Arg (tentative position 32-33) and Ser-Arg (tentative position 75-76). The amino acid sequences of the peptides were determined by the dansyl-Edman method, with the exception of residues 23-25 and 99-102, which were positioned by homology. The enzyme differs in 38 positions from the enzyme from rat and in 31-42 positions from other mammalian pancreatic ribonucleases, while rat ribonuclease differs at 44-52 positions from the other enzymes. These data point to a common ancestry of the enzymes from muskrat and rat and an increased evolution rate of rat ribonuclease after divergence of the ancestors of both species. Muskrat ribonuclease contains no carbohydrate, although the enzyme possesses a recognition site for carbohydrate attachment in the sequence Asn-Val-Thr (62-64).
Insights
Researchers sequenced muskrat pancreatic ribonuclease, revealing evolutionary insights. This enzyme shares ancestry with rat ribonuclease but exhibits a faster evolutionary rate in rats.
Area of Science:
- Biochemistry
- Molecular Biology
- Evolutionary Biology
Background:
- Pancreatic ribonucleases (RNases) are crucial enzymes involved in RNA degradation.
- Comparative analysis of RNase sequences provides insights into evolutionary relationships and rates.
Purpose of the Study:
- To determine the complete amino acid sequence of muskrat (Ondatra zibethica) pancreatic ribonuclease.
- To compare the muskrat RNase sequence with other mammalian RNases to understand evolutionary divergence.
Main Methods:
- Isolation and purification of pancreatic ribonuclease from muskrat.
- Enzyme modification: performic acid oxidation and reduction/aminoethylation.
- Tryptic digestion and peptide analysis using the dansyl-Edman method.
- Sequence determination by homology with known mammalian RNase sequences.
Main Results:
- The complete amino acid sequence of muskrat pancreatic ribonuclease was elucidated.
- Muskrat RNase differs by 38 positions from rat RNase and 31-42 positions from other mammalian RNases.
- The enzyme contains a potential carbohydrate attachment site (Asn-Val-Thr) but lacks glycosylation.
- Sequence data suggest a common ancestor for muskrat and rat RNases, with accelerated evolution in the rat lineage.
Conclusions:
- Muskrat and rat pancreatic ribonucleases share a common evolutionary origin.
- Rat ribonuclease has undergone a more rapid evolutionary rate subsequent to the divergence of these species.
- The presence of a glycosylation recognition site without actual glycosylation in muskrat RNase warrants further investigation.