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  • Based on its kinetic parameters and quaternary structure R

    2024-07-10

    Based on its kinetic parameters and quaternary structure, R. pycnus arginase is a typical ureotelic L-arginase [2]. The Km value of the enzyme was lower than other arginases from other organisms (Table 2), including S. cerevisiae (15.7mM), B. anthracis (10mM), B. caldovelox (3.4mM), human liver (2.3mM) and beef liver (0.95mM). The lower Km value of R. pycnus arginase indicates that the enzyme has a greater affinity for the substrate (L-arginine). In addition, the catalytic efficiency of R. pycnus arginase was relatively high, approximately 3- and 60-fold higher than B. caldovelox and human liver arginase I, respectively. In this study, it was found that L-ornithine had a lower inhibition effect on this recombinant arginase compared with the precious reports [8]. Moreover, the optimal concentration of substrate ranging 150 to 250g/L made this enzyme suitable for high L-ornithine production. The highest production rate of L-ornithine was reported by Song et al. [11]. However, the high concentration of residual L-arginine (more than 30g/L) made the product separation complex. Here, 144.4g/L L-ornithine was obtained within 6h, with only 9.2g/L substrate residue, which demonstrated it to be an efficient L-ornithine production method. In conclusion, the R. pycnus arginase was successfully cloned using degenerate PCR and inverse PCR techniques, and the nuclear and amino sr9011 sequences was firstly reported. R. pycnus arginase showed significant thermostability and high enzyme activity at its optimal pH with Mn2+. Kinetic study showed that this enzyme had higher catalytic efficiency than other arginases reported. Low inhibition of product and high productivity made R. pycnus arginase could be applied in high L-ornithine biosynthesis.
    Competing interests
    Acknowledgements This work was financially supported by the 863 project of China (No. 2013AA102102) and the Fundamental Research Funds for the Central Universities (SKLF-ZZA-201509).
    Introduction Agaricus bisporus (white button mushroom) has high nutritional value and is the world popular cultivated edible mushroom (Meng et al., 2012a). Since this mushroom is characterized by high respiration, its postharvest life is generally no longer than three days at ambient temperature (Mahajan et al., 2008). Considering this fact, research mainly focused on how to prolong storage life to benefit the mushroom industry and the consumers as well. As identified as a naturally occurring plant regulator, methyl jasmonate (MeJA) showed a great potential to retain the postharvest quality of fruits and vegetables. MeJA treatment has been shown to be able to retain higher content of soluble sugars, e.g. fructose, glucose and sucrose and organic acids, e.g. malic acid and citric acid as found in kiwifruit slices (Wang and Buta, 2003) and radishes (Wang, 1998) and to maintain higher content of total phenolic compounds and increased antioxidant capacity as detected in Chinese bayberries (Wang et al., 2009), raspberries (Chanjirakul et al., 2006) and romaine lettuce (Kim et al., 2007). Other than these, MeJA as a potent signaling molecule in plant defense responses, was found to be able to activate the induction of a set of resistance genes during fruit and vegetables storage (Creelman and Mullet, 1997, Zhu and Tian, 2012). It has been demonstrated that treatment of A. bisporus with MeJA vapor at a concentration of 100μmolL−1 can greatly improve the A. bisporus postharvest quality maintenance (Meng et al., 2012a) whereas the regulatory mode underlying this observation remains completely elusive so far. As one of the ornithine cycle enzyme, arginase catalyzes arginine to produce ornithine and urea and plays important roles in nitrogen metabolism of many organisms (Wagemaker et al., 2005). Arginase activity modulates the cellular levels of ornithine and arginine, which are essential for diverse fundamental metabolic processes e.g. biosynthesis of creatine, polyamines (PAs), proline, nitric oxide (NO), glutamate and so on (Gao et al., 2009, Jubault et al., 2008). Besides arginine decarboxylase (ADC) and NO synthase (NOS), arginase is considered as another key enzyme in animal and plant system for arginine catabolism (Zhang et al., 2010, Zhang et al., 2011).