Physiological Mechanism for Enhanced Cyclic Adenosine Monophosphate Salvage Synthesis by Oxymatrine
Objective:When cAMP was synthesized via the salvage pathway,guanosine was also produced in large amounts as a major by-product.In order to enhance cAMP salvage synthesis,an inosine monophosphate dehydrogenase(IMPDH)inhibitor was screened and utilized to reduce by-product production.Methods:The optimum addition conditions for IMPDH were determined by shake flask experiments and the fermentations with oxymatrine addition were carried out in a 7 L fermentor.Then,the fermentation performance,key enzyme activities,by-product levels and transcriptome analysis were systematically investigated.Results:With the addition of 20 mg/L oxymatrine for 24 h,the cAMP concentration reached 4.30 g/L with an increase of 58.67％higher than that of the control,and the fermentation performance was also obviously promoted.The results of enzyme activities and by-product levels showed that IMPDH together with 5'-nucleotidase were strongly inhibited and the enzyme activities for cAMP synthesis were enhanced,obviously leading to higher cAMP levels and lower guanosine production.The transcriptome analysis results showed that due to the addition of oxymatrine,the transcription levels of key enzyme genes in EMP,de novo synthesis and by-product synthesis pathway were significantly decreased,and at the same time,those in TCA cycle,PPP pathway and salvage pathway were significantly increased.Conclusion:Oxymatrine could effectively decrease by-product synthesis and promote cAMP synthesis by regulating metabolism of enzyme activity and transcription level,resulting in more carbon flow and ATP supply directed into cAMP savage pathway for product synthesis.
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