ANHYDRIOBIOSIS 25 



protection depended sharply on the proper ratio between the 

 number of molecules of the protective substance and the number 

 of bacteria. When the number of dried bacteria was increased 

 tenfold, optimal viability was achieved when the quantity of the 

 protecting substance was increased in the same ratio. In the 

 case of Nal, approximately 100 million molecules of this 

 compound per bacterial cell gives optimal protection against the 

 lethal effects of air. 



An attempt was made to fit the heterogeneous data into a 

 coherent hypothesis. It is clear that oxygen does not destroy the 

 dried bacteria by oxidation or the formation of peroxides, since 

 the protecting substances are mostly non-reductants. Moreover, 

 some reducing substances with SH-groups, like glutathione, 

 even enhance the lethal effect. 



Because of the electronic structure of the O2 molecule, we can 

 assume that it is readily reactive with a number of metastable 

 reactive metabolites. The latter may indeed be vital to the cell 

 but ordinarily they are protected from direct attack by dissolved 

 oxygen by the circumstance that oxygen has a low solubility and 

 diffuses in water much more slowly than in a solid phase. 

 Moreover, active metabolism of the cell makes the direct contact 

 of the intermediates with oxygen unlikely. Little more can be 

 said at this stage about the nature of these intermediates. 

 However, it should be mentioned that Commoner detected free 

 radicals in lyophilized biological materials-^. Also artificial free 

 radicals in proteins produced by high doses of X-rays have been 

 found to be stable in vacuo but to react quickly with oxygen and 

 usually to disappear 2-^. It may be possible that these radicals are 

 molecules in a triplet state as suggested by Szent-Gyorgyi-^. He 

 claims that free energy in metabolic processes passes from place 

 to place through substances in the reactive, triplet state {i.e. 

 having electrons with 2 parallel spins). This state is metastable 

 and its life span depends on the conditions prevailing. For 

 instance, the presence of crystalline water or of hydration water 

 around proteins makes it easier for the molecules to pass from 

 singlet to triplet, i.e. to a more reactive state in which they 



References p. 29 



