Fish aminopeptidases from Alaska Pollack roe and tuna

Fish aminopeptidases from Alaska Pollack roe and tuna pyloric caeca have been reported on [12,13]. More recently, we described the purification of a leucine aminopeptidase from the skeletal muscle of the common carp [14], red sea bream [15] and a lysine aminopeptidases from Japanese flounder [16]. The objective of this study was to purify and characterize an aminopeptidase from the skeletal muscle of black carp, and trace the changes of aminopeptidase activity in fish muscle during salting and storage. The possible contributions of aminopeptidases to the generation of free Sulfasalazine and flavor development are discussed regarding Chinese traditional salted fish.
Materials and methods
Results and discussion
Conclusion
Contributors
Acknowledgements We thank Jeff Decile for him proofreading the manuscript. The work was financially supported by the National Natural Scientific Foundation of China (No. 41163004), the Science and Technology Research Foundation of Jiangxi (No. 20112BBF60018) and Jiangxi Agricultural University (No. CX201107), China.
Introduction Aminopeptidase N (APN), also known as CD13, is a Zn2+-dependent enzyme that preferentially removes neutral or basic amino acids from N-terminal of unsubstituted protein and peptide substrates [1]. It plays essential roles in terms of physiological functions, including extracellular matrix degradation, cell motility and angiogenesis [[2], [3], [4]]. It is not only widely expressed in normal mammalian cells, but also found to be overexpressed in most invasive human cancers, especially for the fast-growing and aggressive phenotypes [5]. The APN activity in both tissues and blood have been demonstrated to have a strong correlation with proliferation, invasion and metastasis of tumors, and the increased plasma APN activity has proven the predictive value in the diagnosis and prognosis of the solid tumors, such as breast cancer, thyroid cancer, non-small cell lung cancer, colorectal cancer and pancreatic cancer [[6], [7], [8], [9], [10]]. Therefore, it is in high demand to develop sensitive and selective methods for the detection of serum APN activity, which might be a potential diagnostic and prognostic factor in the tumor-related sensing. To date, there have been a few methods developed for the detection of APN activity, such as nuclear magnetic resonance, bioluminescent imaging and fluorescence [[11], [12], [13]]. However, the existing methods always have the defects of high background signal, complex sample preparation and the need of expensive instruments and reagents. With the instant development of supramolecular chemistry, a series of manmade ring molecules (e.g. cucurbit[n]uril, calixarene and cyclodextrin) are attracting the increasing interests of researchers because of the value in the construction of molecular architectures for biological applications [[14], [15], [16], [17]]. Like those biomolecular recognition systems (e.g. antibody-antigen, avidin-biotin), the manmade ring molecule-mediated host-guest interaction has displayed favorable specificity and high affinity, making it possible for the sensing of some targets in complex samples [[18], [19], [20]]. Among them, cucurbit[8]uril (CB[8]) is a representative cyclic glycoluril-derived ring molecule, which is capable of binding simultaneously to two same or different guest molecules [21]. Therefore, CB[8] has become a popular linker molecules in the fabrication of biosensors based on the formation of CB[8]-mediated ternary complex. For example, Li et al. proposed a versatile way for protein sensing based on the CB[8]-mediated combination of methylviologen and aromatic side chain within the substrate peptide [22]; Yin and coworkers reported a novel electrochemical method for the sensing of protein arginine deiminase 4 with the use of CB[8]-assisted connection of two peptides with FGG for signal labeling [23]; Zhu et al. designed a CB[8]-based rotaxane platform that realized the efficient detection of a broad class of explosives [24].