Fig. 6

Schematic diagram of ammonium-sulfate induced up-regulation of multiple CEs and thereby increased glycosidic bond accessibility. Normally, the transcription factor ThGsfR2 inhibited ThCE3 expression by competitive binding of the functional region of Thce3 promoter. After the ammonium-sulfate addition, AS would be transported into the cell by SULTR and AMT, and ammonium ions were converted to NH₃ by deprotonation, while SO₄²⁻ was reduced into S²⁻ by ATPS. Pyruvate produced by glycolysis bound NH₃ to produce alanine (Ala). Ala would be converted to O-acetyl homoserine (OAHS) by multi-enzyme catalysis. Subsequently, OAHS would be converted to homocysteine (HCY) catalyzed by the O-acetyl homoserine sulfhydrylase, and further catalyzed by 5-methyltetrahydrofolate-homocysteine methyltransferase (metH) to produce the terminal assimilates methionine (Met). Met was converted to AdoMet by ATP activation and induced methylation of the ThgsfR2 promoter, leading to transcriptional repression of ThgsfR2. This allowed Thce3 to be released from the repression of ThGsfR2, exhibiting a significant up-regulation of transcriptional level. In addition, multiple CEs were induced to be up-regulated by unknown inducers generated by AS assimilation. Up-regulation of CEs enhanced polysaccharide deacetylation, which in turn increased hydrophilicity and removed the spatial barrier of glycosidic bonds. 1. Acetylation of xylose residues prevented glycoside hydrolases from glycosidic bonds. 2. CEs catalyzed deacetylation of the xylose acetyl group. 3. Deacetylation removed the spatial barrier of glycosidic bonds and increased the accessibility of the glycosidic bond to glycoside hydrolases