EFFECTS ON PERMEABILITY AND ACTIVE TRANSPORT 



189 



ing marked effects in the dark, and has a mmimal effect on Na+ (Fig. 1-11). 

 Tliese results were interpreted in terms of a Na+ pump operating from gly- 

 colytic energy, the photosynthetic formation of phosphoglycerate in the light 

 counteracting the block by iodoacetate. This suggests that the ATP from 

 the 3-phosphoglyceraldehyde dehydrogenase step is not necessary for trans- 

 port and that energy can come from the metabolism of phosphoglycerate, 

 possibly through pyruvate and the cycle. Similar results have been reported 

 with the red alga Porphyra perforata, except that here iodoacetate causes 

 only a loss of K+, cell Na+ remaining almost unchanged (Eppley, 1958). 



20 22 24 26 



Fio. 1-11. Effects of iodoacetate at 1 n\M and 5 mill on the K^ (broken 



lines) and Na+ (solid lines) levels in Ulva in the light (L) and dark (D). 



(Modified from Scott and HavAvard, 1953.) 



In the light the loss of K+ is much less. The failure to gain Na+ during 

 inhibition is not a characteristic of this organism, since other inhibitors 

 (cyanide, arsenite, and p-chloromercuribenzoate) cause a significant uptake 

 of Na+ as the K+ is lost, so that iodoacetate might be thought of as exerting 

 some more specific action. 



Transport across the Intestinal Wall 



Certain sugars and amino acids are actively transported by the intestine. 

 Iodoacetate can be used to differentiate between substances actively and 

 passively transported (Wilbrandt and Laszt, 1933). Treatment of rat intes- 

 tine with 1.1 mM iodoacetate reduces the amount of glucose lost from the 



