ASCORBATE-IN'DUCED LYSIS OF ISOLATED MITOCHONDRIA 63 



Although reagents reacting with sulphhydryl groups did not mimic 

 ascorbate, it was of considerable importance to determine whether re- 

 action of these substances with the mitochondrial membrane prevented 

 the action of ascorbate. In Fig. 14 it may be seen clearly that ascorbate 

 lysis seems to be independent of the action of /)-hydroxymercuribenzoate. 

 Lysis occurs in a typical fashion whether ascorbate is added simultaneously 

 with or 20 min. after the inhibitor. Similar data have been obtained with 

 arsenite. These data suggest that thiol or dithiol groups may not be critical 

 for the lytic action of ascorbate. 



We have investigated the specificity of the ascorbate type of effect by 

 testing substances structurally related to ascorbate. The ones of primary 



Fig. 15. Formulae for ascorbic acid and some compounds with structures 

 related to part of the ascorbate molecule. 



interest are shown in Fig. 15. Isoascorbate gives an effect identical with 

 ascorbate (Fig. 16). In experiments followed for just 60 min., dehydro- 

 ascorbate, the oxidation product of ascorbate had no effect, but longer 

 experiments revealed that it may produce an effect after very long lag 

 periods (60-90 min.). How much reduction occurs is unknown. The 

 precursor of ascorbate, gulonolactone, does not induce lysis at all. Two 

 compounds containing groups similar to the active oxido-reduction centre 

 of ascorbate, dihydroxyfumarate and dihydroxymaleate, produce lysis 

 which appears identical to that with ascorbate, with one important 

 difference — the lag period is 40-50 min. instead of 15-25. The active 

 concentrations are identical with ascorbate, and other concentrations do 

 not give a shorter lag period. 



Not only do low concentrations of dihvdroxvfumarate and dihy- 

 droxymaleate act like ascorbate, high concentrations, like high ascorbate, 

 do not cause lysis. Moreover, high concentrations of the dihydroxy acids 

 block low concentrations of ascorbate and high concentrations of ascorbate 



