The phosphorylation coupling factors of the chloroplast thylakoid membranes were plucked off to form deficient membranes which were combined with crista membranes to form a fusion system. This membranes reconstituted ...The phosphorylation coupling factors of the chloroplast thylakoid membranes were plucked off to form deficient membranes which were combined with crista membranes to form a fusion system. This membranes reconstituted ATP synthesis activity in light. However, the △pH in the reaction medium was not observed.This paper is a report on some of the results obtained recently in connection with the problem. Various examinations and measurements were used and this phenomenon was repeated. Through the reconstituted system, (thylakoid membranes combined with crista membranes) the kinetic proton changes were studied. It proved that the photophosphorylation activity of this system increased with the increase of the quantity of the combined crista membranes to which, however, the △pH in medium, the effects of 9-AA fluorescence quenching, and the absorption change of neutral red in the membrane pockets were inversely proportional. For this phenomenon, analyses and discussions on the relationship between electron transport or proton transduction and ATP synthesis in the fusion membranes have been made.展开更多
Chloroplast-located proteins which are encoded by the nuclear genome have to be imported from the cytosol into the organelle in a posttranslational manner. Among these nuclear-encoded chloroplast proteins are the ligh...Chloroplast-located proteins which are encoded by the nuclear genome have to be imported from the cytosol into the organelle in a posttranslational manner. Among these nuclear-encoded chloroplast proteins are the light- harvesting chlorophyll a/b-binding proteins （LHCPs）. After translation in the cytosol, precursor proteins of LHCPs are imported via the TOC/TIC translocase, processed to their mature size to insert into thylakoid membranes where they recruit chlorophylls a and b to form pigment-protein complexes. The translocation of proteins is a highly regulated process which employs several regulators. To analyze whether CAO （chlorophyll a oxigenase） which converts chlorophyll a to chlorophyll b at the inner chloroplast membrane, is one of these regulators, we performed import reactions utilizing a homozygous loss-of-function mutant （cao-1）. We imported in vitro translated and 35S-labeled precursor proteins of light- harvesting proteins of photosystem II LHCB1, LHCB4, and LHCB5 into chloroplasts isolated from cao-1 and show that import of precursor proteins and their processing to mature forms are not impaired in the mutant. Therefore, regulation of the import machinery cannot be responsible for the decreased steady-state levels of light-harvesting complex （LHC） proteins. Regulation does not take place at the transcriptional level either, because Lhcb mRNAs are not down-regulated. Additionally, reduced steady-state levels of LHCPs also do not occur due to posttranslational turnover of non-functional LHCPs in chloroplasts. Taken together, our data show that plants in the absence of CAO and therefore devoid of chlorophyll b are not influenced in their import behavior of LHC proteins.展开更多
基金Project supported by the National Natural Science Foundation of China.
文摘The phosphorylation coupling factors of the chloroplast thylakoid membranes were plucked off to form deficient membranes which were combined with crista membranes to form a fusion system. This membranes reconstituted ATP synthesis activity in light. However, the △pH in the reaction medium was not observed.This paper is a report on some of the results obtained recently in connection with the problem. Various examinations and measurements were used and this phenomenon was repeated. Through the reconstituted system, (thylakoid membranes combined with crista membranes) the kinetic proton changes were studied. It proved that the photophosphorylation activity of this system increased with the increase of the quantity of the combined crista membranes to which, however, the △pH in medium, the effects of 9-AA fluorescence quenching, and the absorption change of neutral red in the membrane pockets were inversely proportional. For this phenomenon, analyses and discussions on the relationship between electron transport or proton transduction and ATP synthesis in the fusion membranes have been made.
文摘Chloroplast-located proteins which are encoded by the nuclear genome have to be imported from the cytosol into the organelle in a posttranslational manner. Among these nuclear-encoded chloroplast proteins are the light- harvesting chlorophyll a/b-binding proteins （LHCPs）. After translation in the cytosol, precursor proteins of LHCPs are imported via the TOC/TIC translocase, processed to their mature size to insert into thylakoid membranes where they recruit chlorophylls a and b to form pigment-protein complexes. The translocation of proteins is a highly regulated process which employs several regulators. To analyze whether CAO （chlorophyll a oxigenase） which converts chlorophyll a to chlorophyll b at the inner chloroplast membrane, is one of these regulators, we performed import reactions utilizing a homozygous loss-of-function mutant （cao-1）. We imported in vitro translated and 35S-labeled precursor proteins of light- harvesting proteins of photosystem II LHCB1, LHCB4, and LHCB5 into chloroplasts isolated from cao-1 and show that import of precursor proteins and their processing to mature forms are not impaired in the mutant. Therefore, regulation of the import machinery cannot be responsible for the decreased steady-state levels of light-harvesting complex （LHC） proteins. Regulation does not take place at the transcriptional level either, because Lhcb mRNAs are not down-regulated. Additionally, reduced steady-state levels of LHCPs also do not occur due to posttranslational turnover of non-functional LHCPs in chloroplasts. Taken together, our data show that plants in the absence of CAO and therefore devoid of chlorophyll b are not influenced in their import behavior of LHC proteins.
