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Biomedical subjects

A T Jagendorf

Publications and source records attributed to A T Jagendorf.

7 recordsLinked to original sources
PubMed1992

A homolog of Escherichia coli RecA protein in plastids of higher plants.

Studies of chloroplast DNA variations, and several direct experimental observations, indicate the existence of recombination ability in algal and higher plant plastids. However, no studies have been done of the biochemical pathways involved. Using a part of a cyanobacterial recA gene as a probe in Southern blots, we have found homologous sequences in total DNA from Pisum sativum and Arabidopsis thaliana and in a cDNA library from Arabidopsis. A cDNA was cloned and sequenced, and its predicted amino acid sequence is 60.7% identical to that of the cyanobacterial RecA protein. This finding is consistent with our other results showing both DNA strand transfer activity and the existence of a protein of the predicted molecular mass crossreactive with antibodies to Escherichia coli RecA in the stroma of pea chloroplasts.

Amino Acid Sequence↗
PubMed1977

Arginine modifiers as energy transfer inhibitors in photophosphorylation.

Photophosphorylation by spinach chloroplasts is inhibited after they have been incubated in the dark with either phenylglyoxal or butanedione. Inhibition by phenylglyoxal is strongest when N-ethylmorpholine is the buffer used during the incubation; that by butanedione requires the presence of borate as buffer. The inhibitions are not reversed by simply washing out the inhibitor, suggesting that a covalent modification of one or more arginine residues is responsible. This is supported by the reversibility of the butanedione inhibition if both the inhibitor and borate buffer are removed. ATPase of the chloroplasts, and of extracted protein, is inhibited, whether activated by trypsin or by heating. This indicates that arginine residues of the coupling factor are the probable major site(s) for attack by these modifiers, leading to the observed inhibitions.

Aldehydes↗
PubMed1977

Lack of site-specificity of spinach chloroplast coupling factor 1.

The irreversible inhibition of chloroplast phosphorylation by either sulfate anions, or N-ethylmaleimide, is energy dependent. Chloroplasts must first be illuminated in the presence of the inhibitors and a mediator of electron flow, for the subsequent phosphorylation to show any inhibition. Both inhibitors affect the chloroplast coupling factor 1. Electron transport only through Photosystem I can be used to activate either of these inhibitions. The subsequent inhibition in a second light reaction is the same whether ATP synthesis is supported by Photosystem I, or by Photosystem II electron transport. The reverse experiment, activating inhibition by electron transport only through Photosystem II, is possible in the case of sulfate. Again, the inhibition is expressed whether Photosystem II or Photosystem I electron flow supports ATP synthesis. We conclude that the two electron transport regions of probably generate the same high energy state which is able to activate all members of a functionally uniform coupling factor population. These enzyme molecules must catalyze phosphorylation coupled to electron transport through either region of the chain. The results tend to discredit models requiring a separate group of coupling factor molecules unique to each part of the chain.

Binding Sites↗
PubMed1975

Chloroplast membranes and coupling factor conformations.

The demonstrated role of proton translocation and resulting electrochemical activity gradients (protonmotive force) in ATP synthesis by chloroplasts is noted. Evidence for the participation of conformational changes in the terminal ATPase (coupling factor, or CF1) is reviewed. Hydrogen exchange into ordinarily cyptic groups of the molecule occurs only when the subtending membranes are put under the stress of a protonmotive force. Since up to 100 hydrogen atoms per mole are involved in the energy-dependent exchange the conformational change permitting tham access to the medium must be a major one. Chemical reagents are beginning to be used to attack groups on CF1 that are exposed only when the membranes are energized. N-ethylmaleimide binds covalently, sulfate causes as yet unspecified damage, and permanganate leads to oxidative damage to CF1 under energized conditions. The last two reagents are analogues of phosphate, and ADP must be added for them to inhibit. On the basis of this and other differences between the conditions needed for inhibition by permanganate or sulfate, and that by N-ethylmaleimide or the hydrogen exchange, a somewhat complex scheme involving several successive or alternative conformations of CF1 can be postulated. Questions are raised as to the way in which a conformational change in a bound protein could be caused by a proton activity gradient across its supporting membrane, and as to whether the altered conformations might constitute a part of the energy transformations leading to ATP synthesis.

Adenosine Triphosphatases↗