577 



Jerome J, WoU^en 



tochrorae-552 is not a resiilt of a non- uniform synthesis of chloro- 

 phyll, since sufficient Euglena remained chlorophyll-free during 

 the first 2^ hrs. of liglit exposure to permit the extraction of a 

 high concentration of cytochrome -55 6. This spectral species of 

 c;>'tochrome must have heen isolated from cells in which active chl- 

 orophyll synthesis was occurring. The concentration of cytochrome 

 -556 remains relatively constant {k x lOT m moles per gram wet 

 weight of cells); however, cytochrome-552 increases directly with 

 chlorophyll synthesis in a ratio of the order of 1 c;i'tochrome-552 

 to every 300 chlorophyll molecules. The change-over from one 

 spectral type of cytochrome to the other would be expected to oc- 

 cur earlier than it has been observed. Cytoclirome-552 is prob- 

 ably synthesized fran a common metabolic pool under the influence 

 of light. Both c;!,'tochromes are therefore present in the photosyn- 

 thetic Euglena . 



Ifeinometric measurement of the photosynthetic-respiratory ratio 

 (p/R) shows that until dark-grown Euglena have been illuminated 

 for 2k hrs,, the P/R = <1. After this time (at least one genera- 

 tion, varying between I6 and 2^ hrs-) v the P/R becomes >1 and ac- 

 tive photosynthesis can be measured^ ', These data are in agree- 

 ment with our observations on the increase of chlorophyll and the 

 chlorophyll dependence of c-^d:ochrome-552^°^. 



The oxidation-reduction potential E'q of c:>'tochrome~552 is 

 +0,38 volts, and for cytochrome -5 5 6 is +0.32 volts. These high 

 potentials for the c;>'tochromes indicate that they can take part 

 in the photometabolic electron transport in the cloloroplast. IIo\7-- 

 ever, in view of the measured value of the oxidation-reduction po- 

 tential for cytochrome-55'J> which is greater than that expected 

 for the respiratory cytochrome-£ as well as for cytochrome-a + ao 

 it could not transfer electrons to the oxidase; i.e., it could 

 not be oxidized by the enzyme. It is suggestive, then, that cy- 

 tochrome-556 is associated with the initial steps leading to chl- 

 orophyll synthesis and to the chloroplast structure, V"^ 



STRUCTURE 



To bring the chemistry of the chloroplast together with its 

 struct lire, a morphological study of Euglena chloroplast s under 

 different environmental conditions lias been pursued. In the light 

 microscope, Euglena chloroplasts are easily identified as green 

 organelles (see Fig. ^, a cross-section of a Euglena ), Electron 

 microscopy increases the resolution to delineate a chloroplast 

 membrane and internal dense layers (lamellae) with less dense in- 

 terspaces (Fig, 6), Each dense layer is of the order of 25O A in 



