The primary structures of pancreatic ribonucleases from African porcupine and casiragua, two hystricomorph rodent species.

The amino acid sequences of the pancreatic ribonucleases from African porcupine (Hystrix cristata) and casiragua (Proechimys guairae, a caviomorph rodent species related to the coypu) were determined. The ribonucleases were isolated form minces of pancreatic tissue which had been used for the extraction of the insulins. The results of the sequence determinations of residues 67-78 in both enzymes were ambiguous. Therefore, homology with other ribonucleases has been used in deriving these sequences. At position 94 aspartic acid was found, while all other ribonuclease sequenced to date have asparagine at this position. This may indicate a specific deamidation as a result of the acidic conditions during the extraction of insulin. The amino acid sequence of African porcupine ribonuclease shows a close relationship with those of the South-American caviomorph rodents, which implies that the hystricomorph suborder of the rodents, to which both the African porcupine and the caviomorphs belong, is a natural (evolutionary) taxon. Both porcupine and casiragua ribonuclease are glycoproteins with complex-type carbohydrate chains attached to asparagine-34.