FISHERY BULLETIN: VOL. 73, NO. 2 



It is sufficient to simply state that the unpaired 

 electron is localized on nitrogen and this localiza- 

 tion resides primarily in a p-orbital on nitrogen. 

 p-Orbitals are dumbbell-shaped electron density 

 regions in space, and the magnetic properties as- 

 sociated with an electron in such an orbital 

 depends on the so-called tumbling frequency of 

 the electron (how fast the p-orbital assumes a 

 random distribution of orientations while part of 

 the nitroxide in a biological system). An example 

 of two limiting situations is shown in Figure 4. 

 Spectrum 4A was recorded for a nitroxide in liquid 

 glycerol, while 4B is for the frozen solution. Spec- 

 trum 4A tells us that moderate fast tumbling 

 prevails, while 4B shows tumbling to be essentially 

 quenched. The reader is referred to the literature 

 (Roubal 1972) for a more thorough discussion on 

 the dependency of spectral characteristics on 

 tumbling frequency (label mobility). 



Intermediate mobilities are characterized by a 

 family of spectra. Examples are to be found in the 

 recent spin-labeling study of a hapten combining 

 site of trout antibody by Roubal et al. (1974). Using 

 appropriate mathematical manipulations of 

 recorded spectra, one can measure tumbling 

 frequencies with accuracy. These frequencies 

 together with other derived data provide quanti- 

 tative characterization of labeling studies. 



MEMBRANES AND 

 MEMBRANE PROPERTIES 



The importance of membranes in biological 

 roles of living systems cannot be overemphasized. 

 Membranes, as mentioned, are responsible for 



Figure 4.-Label II (see text) in glycerol. 



A. In liquid glycerol at room temperature. 



B. Frozen in glycerol at liquid nitrogen temperature. 



Label mobility (effect of environment) is calculated by 

 measurements of line widths, heights, intensity ratios, and 

 spacing. 



neural function. Membranes participate in ion- 

 binding and in governing tissue permeability. As- 

 sociated with membranes, especially mi- 

 tochondrial membranes, are a variety of enzymes. 

 Cytochrome oxidase and other electron transport 

 enzymes are membraneous in nature. Membrane- 

 bound enzymes require the proper conditions such 

 as lipid fluidity, proper phase transition tempera- 

 tures, and lipid-protein interactions for their 

 function. The participation of membranes in 

 neural control is well documented. Neural 

 membranes contain molecular size pores which 

 mediate sodium /potassium transport. The exact 

 nature of these pores has not been delineated 

 completely, but several lines of evidence suggest 

 that pores consist of a cagelike arrangement of 

 protein which spans the membrane from the inner 

 to the outer surface. Membranes are considered to 

 be the basis of life itself. 



Membranes consist principally of proteins and 

 lipids. Carbohydrates comprise 0-10% of the 

 membrane mass. Lipids account for about 40% of 

 the mass, and the balance is protein. Membranes 

 are a matrix of lipids and proteins arranged in a 

 bimolecular leaflet (Singer 1972; Green 1972), 

 illustrated in Figure 5. The little circles represent 

 phospholipid headgroups (choline, ethanolamine, 

 serine, phosphatidic acid, etc.) while proteins are 

 indicated by the larger "islands." Interspersed 

 with the fatty acid tails (squiggly lines) are sterols 

 and lesser tissue lipid components. Typical 

 membranes are about 100 A thick. 



Membrane lipids are amphiphilic-provided 



FiGURK 5. -Membrane bilayer leaflet. Small circles represent 

 phospholipid headgroups. Squiggly lines are fatty acid tails. 

 Large islands represent membrane protein. From Singer 1972. 

 (Courtesy of S. J. Singer and New York Academy of Sciences.) 



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