4. Analysis of gene expression related to phycocyanin synthesis by rGO-TiO2
The regulation of the metabolic synthesis of phycocyanin inFACHB-314 can be assessed by gene expression level analysis. In this study, we choose three key synthetase enzymes that can regulate the synthesis of phycocyanin: The gene encodes urinary hyaluronan III synthase (CobA-hemG), which can promote the production of urobilin III, which is an important tetrapyrrole intermediate, including the synthesis of chlorophyll, vitamin B12, heme and bilinin (Doan et al., 2021; Faieta et al., 2021). HemG gene encodes protoporphyrinogen IX oxidase, which can catalyze oxidized protoporphyrinogen IX to produce protoporphyrin IX (Li et al., 2017; Lupatini et al., 2017). The gene encodes heme oxygenase (Ho), which catalyzes the opening of the heme ring structure to form chlorophyll IX, an intermediate in the biosynthesis of bilinin (Liu et al., 2019; Rosa et al., 2019). Under the same conditions, compare the control group and the nanoparticle addition experimental group, and evaluate the regulation and influence mechanism of the material on the synthesis of phycocyanin from the gene expression level as shown in Figure 12 (a).
Figure 12 (b) shows the effect of the phycocyanin synthesis and metabolism pathway in FACHB-314 cells on the gene expression levels of CobA-hemG, HemG and Ho three enzyme proteins after the experimental group and the control group were cultured for 72 hours.
Compared with the control group, the transcript expression levels of CobA-hemG, HemG and ho genes in the FACHB-314 group containing rGO-TiO2 composite nanoparticles were significantly higher than those in the control group, which were 7.57, 5.65 and 3.33 times. The significant differences in the transcriptional expression levels of the three key genes in the phycocyanin synthesis pathway can be explained as follows: the mechanism of rGO-TiO2photocatalytic nanoparticles to promote phycocyanin synthesis inFACHB-314 cells is by stimulating the overexpression of genes encoding key enzymes in the biosynthetic pathway of phycocyanin, thereby promoting a lot of synthesis of CobA-hemG, HemG, and Ho enzyme proteins during the synthesis and metabolism of phycocyanin. Furthermore, theFACHB-314 of the experimental group was induced to increase the accumulation of phycocyanin. The results of the difference in phycocyanin gene expression between the experimental group and the control group are consistent with the above results, that is, rGO-TiO2 photocatalytic nanoparticles can significantly increase the content of phycocyanin in FACHB-314 under red light conditions. The above results clarify from the level of gene transcription and expression that rGO-TiO2photocatalytic nanoparticles sequentially promote the synthesis of uroporphyrinogen III, protoporphyrin IX and biliverdin IX intermediates through enzymatic reactions, thereby increasing the synthesis of phycocyanin.