FISHERY BULLETIN: VOL. 73, NO. 2 



the spectrum for one sample was obtained, the 

 tissue was returned to a large volume of fresh, cold 

 buffer to which test hydrocarbon (in separate 

 tests) was incorporated via sonication. Final 

 hydrocarbon concentration in buffer was 15-25 

 ppm. Hydrocarbons included benzene, toluene, 

 ethyl benzene, hexane, heptane, octadedecane, and 

 cyclohexane. Actual uptake of paraffin hydrocar- 

 bon by tissue membrane, as measured by gas- 

 liquid chromatography (GLC), was on the order of 

 1 ppm. Aromatics were present in higher amounts 

 (5-10 ppm). Tissue was exposed to hydrocarbon in 

 buffer for 1 h. At the end of this period, tissues 

 were withdrawn, rinsed well, and the EPR spectra 

 were re-recorded. 



A comparison of the in vitro spectra for controls 

 with those same samples after hydrocarbon treat- 

 ment provided evidence that a differentiation in 

 binding sites for paraffins and aromatic com- 

 pounds does indeed exist (Figure 7). 



DISCUSSION 



We can explain rather easily the preference of 

 paraffins seeking the interior of membranes- 

 paraffins are nonpolar, very soluble in neutral 

 hydrocarbons, such as those which comprise the 

 hydrogen-carbon chains (or tails) of phospholipid 

 fatty acids. Hence, thermodynamically, system 

 stability is enhanced by mutual interaction of 

 paraffin hydrocarbon with lipid tails. 



Aromatics, on the other hand, are unique, for in 

 addition to their ready solubility in many organic 

 environments, aromatic compounds are fashioned 

 from conjugated double bond systems with pi- 

 electron unsaturation. These factors give aromat- 

 ics the ability to form quasi-chemical complexes 

 with other molecules which can act in electron ac- 

 ceptor-donor roles. 



The surface of the membrane contains many 

 different sites, both polar, nonpolar, and electron- 

 interactive. It appears that some of these sites 

 contain the necessary properties which make 

 binding of aromatics possible. A charge-transfer 

 mechanism (Kier 1971) may direct aromatics away 

 from the membrane interior to the surface. 



These site preferences for paraffins and aromat- 

 ics may account in part for the differences we 

 observe for retention of these substances in living 

 tissue. For instance, in other studies (Roubal 

 1974b) we have shown via GLC, spin-labels, and 

 radiotracers that paraffins are retained in living 



tissue for long periods of time; aromatics are not. 

 What is more, paraffins are relatively nontoxic, 

 while aromatics generally are quite toxic, even at 

 low levels. 



The molecular basis for physiological 

 phenomena is associated in a very direct way with 

 important membrane properties. Ion-binding, 

 lipid protein (enzyme) interaction, lipid phase- 

 transition temperatures, and lipid fluidity are all 

 involved in one way or another. Membrane disor- 



LABEL I 



LABEL II 



Figure 7.-Spin-label spectra of aromatic-treated and paraffin- 

 treated coho salmon spinal cord (SC). 

 SC + Label I ( + treatment). 

 SC + Label II (+ treatment). 

 SC + Label III (+ treatment). 



Changes in the A/R (line height) ratio, narrowing of peak widths 

 (W), and shifts in distance D to lesser values provide data for 

 characterizing influence of treatments (Roubal 1972; Roubal 

 1974a). C, spinal cord control. 

 AR, treatment by aromatics. 

 PAR, treatment by paraffins. 



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