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Quantum requirement of photosystem I mediated ATP formation in chloroplast fragments
Author(s) -
Neumann J.,
Arntzen C.J.,
Dilley R.A.
Publication year - 1971
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(71)80122-9
Subject(s) - tel aviv , von neumann architecture , library science , chemistry , mathematics , computer science , pure mathematics
Light dependent ATP formation in chloroplasts is coupled to electron transport. The number of quanta required to form a molecule of ATP in various types of electron transport may contribute to our understanding of the nature of coupling of ATP to electron transfer [l] . In contrast to electron transport the light intensity curve for photophosphorylation shows a distinct lag [2,3]. Large quantum requirements observed in early studies [2] might have been due to lack of appreciation of this low intensity lag. In addition, in ATP formation, which is supported by ‘cyclic’ electron flow, an initial reduction of the added carrier is required [4] and a proper oxidation-reduction ‘poise’ should be maintained in order to obtain maximal rates of ATP formation [ 1 ] . Sakurai, Nishimura and Takamiya [3] suggested that a pool of high energy intermediates should be filled before photophosphorylation could proceed. Schwartz [5], provided evidence that a build up of proton gradient precedes phosphorylation. He has shown that below a critical actinic light intensity, no ATP synthesis occurs although the proton gradient is formed. Similar observations were made by Dilley [6] . It has been shown that subchloroplast particles (SCP) enriched in System I obtained by the use of digitonin and differential centrifugation support high rates of PMS catalyzed cyclic phosphorylation but their proton pump activity is highly reduced [7]. Recently, we have observed that membranous vesicles derived from the stromal lamellae of spinach chloro-