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Mechanistic insights into pH-dependent H2 photoproduction in bisulfite-treated Chlamydomonas cells.

ABSTRACT: Background:Bisulfite addition is an important H2 photoproduction strategy that removes O2 and activates hydrogenase. The pH values of cell cultures can change the ratio of bisulfite to sulfite, which may affect H2 photoproduction. However, little is known regarding the pH effect of bisulfite addition on H2 photoproduction and relevant underlying mechanism. Results:Here, changes in H2 photoproduction with different initial extracellular pH values showed a parabolic distribution and a pH of 8.0 is an optimal value for H2 photoproduction in Chlamydomonas reinhardtii cells treated with bisulfite. Compared to the growth pH (pH 7.3), increased photoproduction of H2 at this optimal pH was primarily caused by a relatively high residual activity of photosystem II (PSII), which provides a relatively plentiful source of electrons for H2 photoproduction. Such increased H2 photoproduction was most likely a result of decreased the ratio of bisulfite to sulfite, consistent with the result that the toxicity of bisulfite on PSII was much more than that of sulfite. This possibility was corroborated by the result that treatment with a combination of 7 mM bisulfite and 6 mM sulfite further enhanced H2 photoproduction compared with 13 mM bisulfite alone. Conclusions:Collectively, our findings provide novel mechanistic insights into pH-dependent H2 photoproduction in C. reinhardtii cells treated with bisulfite, and demonstrate that sulfite addition is another important strategy for H2 photoproduction, just like bisulfite addition.

SUBMITTER: Wei L

PROVIDER: S-EPMC7132995 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:pH-responsive peptides are promising therapeutic molecules that can specifically target the plasma membrane in the acidified extracellular medium that bathes cells in tumors. We designed the acidity-triggered rational membrane (ATRAM) peptide to have a pH-responsive membrane interaction. At physiological pH, ATRAM binds to the membrane surface in a largely unstructured conformation, while in acidic conditions it inserts into lipid bilayers forming a transmembrane helix. However, the molecular mechanism ATRAM uses to target and insert into tumor cells remains poorly understood. Here, we determined that ATRAM inserts into cancer cells with a preferential membrane orientation, where the C-terminus of the peptide traverses the plasma membrane and explores the cytoplasm. Using biophysical techniques, we determined that the membrane interaction of ATRAM is contingent on the concentration of the peptide. Kinetic studies showed that membrane insertion occurs in at least three steps, where only the first step was affected by the membrane density of ATRAM. These observations, combined with membrane binding and leakage data, indicate that the interaction of ATRAM with lipid membranes is dependent on its oligomerization state. SPECT/CT imaging in mice revealed that ATRAM accumulates in the blood pool, where it has a prolonged circulation time (> 4?h). Since fast peptide clearance and degradation in circulation are major problems for clinical development, we studied the mechanism ATRAM uses to remain in the blood stream. Using binding and transfer assays, we determined that ATRAM binds reversibly to human serum albumin. We propose that ATRAM uses albumin as a carrier in the blood stream to evade clearance and proteolysis before interacting with the plasma membrane of cancer cells. We also show that ATRAM is able to be deliver liposomes to cells in a pH dependent way. Our data highlight the potential of ATRAM as a specific therapeutic agent for diseases that lead to acidic tissues, including cancer.

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Mechanistic insights into pH-dependent H2 photoproduction in bisulfite-treated Chlamydomonas cells.

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