INFLUENCE OF THYLAKOID PROTEIN-PHOSPHORYLATION ON EMERSON ENHANCEMENT AND THE QUANTUM REQUIREMENT OF PHOTOSYSTEM-I

The relative size of the antennae of PS I and PS II has been estimated from 420 to 722 nm in isolated granal thylakoids, by measuring electron transport from H2O to NADP upon flash actinic illumination under conditions of linearity of electron transport versus light intensity. Emerson enhancement of NADP reduction by PS I-absorbed radiation of 722 nm had a large peak at 475-500 nm, dropping to zero at 520 nm, and a minor one at 650 nm. No enhancement was observed from 520 to 640 nm, nor at wavelengths above 670 nm. Phosphorylation of LCH-II suppressed the enhancement at all wavelengths: upon phosphorylation, the antenna of PS I became larger than that of PS II over the entire spectrum, including the 475-500 nm region. The quantum requirement of PS I was measured from 420 to 691 nm in the granal thylakoids. A minimum was observed at 520 nm, and maxima at 475 to 500 and 650 to 670 nm, i.e., corresponding to the LHCII maximal absorption.