THE CENTRAL PROBLEMS OF THE BIOCHEMISTRY OF CELL DIVISION 491 



Tetrahymena cell which divides by a mechanism different from ordinary 

 mitosis, Plesner [45] has demonstrated a build-up of nucleoside triphos- 

 phates in anticipation of division. As I have pointed out elsewhere [i], the 

 principle of an energy reservoir for division need not necessarily be inter- 

 preted in terms of a tangible pool of high-energy compounds, and in fact 

 there are some difficulties with this simple view. Another possibility is that 

 the mitotic apparatus itself is the energy reservoir in the sense that it is 

 assembled in an activated form, and is driven through its manoeuvres by 

 environmental changes such as the SH cycle discussed above. 



Another and simple way of attacking the energetics of cell division has 

 sound precedents. This is the examination of its reactions with ATP or 

 other conventional energy sources. No event in the historv of the bio- 

 chemistry of muscle contraction was more portentous than the discovery 

 by Engelhardt and Ljubimova that the proteins involved in contraction 

 included an ATPase acti^"ity, even though the outcome was not as simple 

 as might have been hoped. It is natural to ask the same question of the 

 mitotic apparatus, and this became possible when the DTDG method 

 became available. Xo ATPase actixity could be obtained with the mitotic 

 apparatus isolated by the alcohol digitonin method. The studies with the 

 new method were begun by Dr. R. M. Iverson and completed bv Dr. R. R. 

 Chaffee. Using straightforward methods of assay analogous to those used 

 for muscle and mitochondrial ATPases, the following information has been 

 obtained, and will be published in full elsewhere, (i) \\'hen the mitotic 

 apparatus is isolated and purified by the DTDG method, dissohed in 

 isotonic KCl, the supernatant following high-speed centrifugation shows 

 a substantial ATPase activity. The sediment, representing the particles 

 associated with and embedded in the apparatus, also shows an activity 

 attributable to yolk, etc., but it has different properties with respect to 

 metal activation, etc. It is assumed, for the present, that the activity of the 

 supernatant is that of the "fibrous" component of the apparatus, which is 

 dissolved in the isotonic KCl. (2) The pH optimum is about 8-4. (3) The 

 activity is highly dependent on divalent ions, and Alg^ " is three times as 

 effective as Ca"^. Manganese is slightly less efl'ectixe than magnesium. 

 (4) The enzyme does not split ADP or glycerophosphate. (:;) The enzyme 

 is highly specific for ATP. It does not split UTP, CTP,^or GTP. The 

 splitting of ITP proceeds at a rate half that of ATP or less. I do not know 

 whether there is a precedent for this degree of ATPase specificity. 



So far, no other enzyme of the mitotic apparatus has been studied. 

 Whether the disco\ ery of a rather specific ATPase is important for our 

 picture of cell division obviously depends on our point of view. It does 

 seem to link the mitotic apparatus to muscle and certain other motile 

 structures such as flagella, by analogy at least, ^^> are bound to suspect 

 that the energetics of mitosis are conventional enough to in\"ol\-e the 



