Antioxidative enzymes such as SOD and
Antioxidative enzymes such as SOD and CAT play prominent roles in protecting against oxidative stress and extending food freshness due to their ability in scavenging active oxygen species for maintaining cell membrane integrity. Evidence shows that activities of SOD and CAT are positively affected by MeJA in postharvest horticultural crops (Chanjirakul et al., 2006, Chanjirakul et al., 2007). Our results also confirmed these findings since we found that the activities of SOD and CAT greatly increased in MeJA-treated fruiting bodies along with the storage (Fig. 5). However, the action of these enzymes in MeJA-treated fruiting bodies was almost diminished upon inhibition of arginase activity by nor-NOHA, indicating that the activities of antioxidant enzymes improved by MeJA at least partly via induction of arginase. In addition, functional components including phenolic compounds and flavonoids are also reported as key factors for mushrooms antioxidant properties (Barros et al., 2008). Our study showed that MeJA positively affected phenolic and flavonoid accumulation in postharvest mushroom (Fig. 6), which may further promote the improvement of antioxidant status in this white mushroom. As compared with MeJA-treated mushrooms, the accumulation of phenolic compounds and flavonoids in mushrooms with combination treatment with nor-NOHA was strongly inhibited during the entire storage. Moreover, both phenolic and flavonoid contents in mushrooms treated with a combination of nor-NOHA and MeJA were found even lower (0.05) than the control group over the most storage periods. These results revealed that the induction of antioxidant components by MeJA was largely attenuated by nor-NOHA. Other than this, the inhibition of arginase may suppressed the hydrolyzation of arginine to ornithine and thus prevented the biosynthesis of polyamine which are capable of maintaining functional components (Champa et al., 2015, Jahangir et al., 2011, Razzaq et al., 2014).
Acknowledgments This work was supported jointly by grants from National Natural Science Foundation of China(No. 31501544), Natural Science Foundation of Tianjin City (No. 17JCQNJC14400) and International Center for Genetic Engineering and Biotechnology (ICGEB) (No. CRP/CHN15-01).
Introduction l-Arginine is a semi-essential amino UNC 3230 receptor derived from dietary intake, whole-body protein breakdown, or endogenous de novo production (Luiking et al., 2002, Wu and Morris, 1998). It is a common substrate of both nitric oxide (NO) synthase (NOS) and arginase. While NOS catabolizes l-arginine into l-citrulline and NO that has various roles in multiple physiological functions, arginase transforms l-arginine into l-ornithine and urea. There are two distinct isoforms of arginase that share ~60% sequence homology: arginase 1 (Arg1) and arginase 2 (Arg2). Arg1 is a cytosolic enzyme predominantly expressed in the liver, as part of the urea cycle, but is also present at lower levels in various extrahepatic tissues including endothelial and vascular smooth muscle cells, with a main role in the production of l-ornithine for polyamines biosynthesis. Arg2 is a mitochondrial enzyme widely expressed in extrahepatic tissues, especially kidney (Morris, 2007, Pernow and Jung, 2013). The physiological roles of this isoform are not well characterized but it is probably involved in the control of NO, polyamines and l-proline production (Morris, 2005). The incidence and prevalence of cardiovascular diseases, reduced kidney function, impaired cognition and chronic obstructive pulmonary disease (COPD) increase abruptly with advancing age (Fontana, 2009). Arguments exist for the involvement of failure in NO production/availability in these diseases (Puca et al., 2012) even though the underlying mechanisms are not well known but likely involve the modulation of arginase pathway. Age-related NO deficiency could result from increased arginase activity since arginase and NOS are in competition for their common substrate l-arginine (Katusic, 2014, Santhanam et al., 2008). Consistently, although poorly studied, arginase activity in the heart (Khan et al., 2012), vessels (Berkowitz et al., 2003, White et al., 2006) and perirhinal cortex (Gupta et al., 2012) was found higher in aged than young rats. An additional mechanism might relate to l-arginine deficiency as evidenced by lower plasma l-arginine levels in aged animals or in elderly people (Ming and Yang, 2013, Morris, 2009, Reckelhoof et al., 1994). In line with such mechanisms are the beneficial effects of l-arginine supplementation on endothelial function (Böger and Ron, 2005, Lerman et al., 1998), kidney function (Reckelhoff et al., 1997) and cognition (Pan et al., 2013) in aged animals and elderly subjects as well as the improvement of spirometry parameters by l-arginine supplementation in COPD patients (Pratap et al., 2016). However, relevance of l-arginine supplementation remains controversial in ageing as l-arginine supplementation was reported to have no effect on vascular function (Blum et al., 2000, Gates et al., 2007, Oomen et al., 2000) and even to induce cardiovascular complications and mortality (Schulman et al., 2006, Wilson et al., 2007). These controversial effects of l-arginine supplementation might relate to a deviation of l-arginine metabolism towards production of l-ornithine rather than NO as a result of Arg1 and/or Arg2 overexpression, as suspected from in vitro studies (Scalera et al., 2009, Xiong et al., 2014). However, whether l-arginine supplementation might increase arginase activity/expression in ageing remains an outstanding issue.