Human spectrin. V. A comparative electro-optic study of heterotetramers and heterodimers

The electrically induced birefringence of human spectrin heterotetramer and heterodimer solutions at 5 degrees C has been studied. 1. The steady-state birefringence, delta, was found to be approximately proportional to the electric field strength, E, when E greater than or equal to 0.2 kV/mm. For spectrin solutions the specific linear coefficient, delta/(E x c), therefore is a more relevant parameter for describing birefringence saturation behavior when E greater than or equal to 0.2 kV/mm than the commonly used Kerr constant. At 5 degrees C were measured delta/(E x c) = (27 +/- 5) x 10(-8)m4 x V(-1) x kg(-1) for heterodimers and heterotetramers. 2. At 5 degrees C both heterotetramers and heterodimers exhibited more than one birefringence relaxation time and the shortest of these was for both molecules found to be 4.2 +/- 1.0 microseconds. This indicates that the spectrin molecules are highly flexible. The birefringence build-up time for heterotetramers and heterodimers was found to be 20 +/- 7 microseconds and 15 +/- 5 microseconds, respectively.