STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 



65 



suggests the absence of the lipid-rich membranes of an endoplasmic reticulum 

 in these tissues. However, the reticulum does appear to exist in the petioles 

 of silver beet and the roots of germinating wheat (Hodge et al., 1957). The 

 cytoplasnwc fractions of various leaves have also been studied in the ultra- 

 centrifuge (Singer et al., 1952; Eggman et al., 1953) and have revealed a 

 number of major particulate components possessing relatively low sedi- 

 mentation coefficients. 



100 



0-1 0-2 03 0-4 0-5 



percent deoxycholate (pH 7-5) 



Fig. 9. Effect of deoxycholate on the biochemical composition of liver microsomes. 

 The microsomes were obtained from rat liver homogenized in 0.88 M sucrose (centri- 

 fugation: 60 minutes at 105,000 g). They were resuspended in 0.88 M sucrose containing 

 the amounts of Na deoxycholate (pH = 7.5) indicated. The treated suspensions were 

 recentrifuged immediately for 120 mmutes at 105,000 g and the pellets thus obtained 

 analyzed chemically. The results, given per gram tissue equivalent, indicate what per 

 cent of the original material is still sedimentable after deoxycholate treatment. (Palade 

 and Siekevitz, 1956.) 



Key: ■ fl, RNA; A k, protein N; •■ «, phospholipide P; 



A — A, liemochromogen; O — -O. DPNH-cytochrome c reductase activity. 



The microsomal fraction contains 16 % of the total sohd in mammahan 

 hver and about 25 % of the total nitrogen in bacteria. This fraction from 

 guinea pig liver contains 9.6 % N and 1.5 % P, being rich in ENA. It has 

 40 to 45 % hpid, of which about two-thirds is a complex mixture of phos- 

 phohpids. Among the fractionated hver and Polytomella microsomes, the 

 smallest particles are richest in ENA. The more homogeneous bacterial 

 particles may contain up to 60 % ENA; the yeast particles are reported to 

 contain 50 % ENA. 



