Protein Uptake by Pinocytosis in Amoebae : Studies 

 on Ferritin and Methylated Ferritin* 



V. T. Nachmias and J. M. Marshall, jR.f 



Department of Anatomy, School of I\Iedhine, 

 University of Pennsylvania, Philadelphia, Penn., U.S.A. 



It has been suggested that pinocytosis may be the underlying process in 

 many transport phenomena. The idea has been reviewed by Dr. Holter, in 

 this Symposium and elsewhere [i]. Such a view seems to have been 

 especially attractive to electron microscopists, who have found evidence 

 for vesicle formation in a variety of cells. Physiologists, however, who have 

 studied and defined active transport by other methods, have felt that the 

 engulfment of droplets of the cell's environment is too indiscriminate a 

 process to account for the highly specific effects which, as Dr. Davis has 

 pointed out in his review for this Symposium, are characteristic of active 

 transport. There are other equally serious inadequacies in the notion that 

 pinocytosis is simply the morphological equivalent of active transport. 



The chief difficulty in this debate is a familiar one ; so long as we do 

 not understand the mechanisms of pinocytosis, on the one hand, or of 

 active transport, on the other, we are free to launch hypotheses which can 

 soar quite freely. The purpose of this communication is therefore to 

 describe experiments which were designed to answer two questions about 

 protein uptake by pinocytosis in amoebae. First, what is the physical 

 mechanism of protein binding to the cell surface, the binding which is 

 known to set off the pinocytosis response ? And second, what happens to 

 the pinocytosis vesicle, and to its contents, after it is taken into the cell ? 

 Note that these questions concern only the first and last stages of the 

 pinocytosis response; between these there occurs the actual process of 

 invagination, the formation of tunnels and vesicles. This must also be 

 studied experimentally, but it will be seen from the results that the first 

 and last stages are those most directly related to the problem of transport 

 between the environment and the cytoplasm. 



The studies of Schumaker [2] and of Brandt [3] supplied the first 

 evidence that protein uptake by amoebae began with some type of binding 



* This investigation was supported by Grant C-1957 from the National Cancer 

 Institute of the National Institutes of Health, United States Public Health Service. 

 t Scholar in Cancer Research of the American Cancer Society, Inc. 



