NUMERICAL-ANALYSIS OF THE ROTATIONAL RELAXATION-TIME OF SPECTRIN SEGMENTS AND SPECTRIN HETERODIMER IN DILUTE AQUEOUS-SOLUTION

The rotational relaxation time for different models of the spectrin al pha beta-heterodimer and spectrin subunits were obtained through numer ical simulation making use of the so-called rigid-body approximation. Based on information on the helix structure of the 106 aminoacids in t he repeating motif of spectrin, three different models with varying de gree of refinement were set up to represent the spectrin subunits: the two-bead, the many-bead and the shell model. For one- and two-subunit spectrin the relaxation time was found to be 20 +/- 4 ns and 92 +/- 5 ns, respectively. The last result conforms well with available experi mental data from transient electric birefringence measurements. For th e alpha beta-heterodimer two different models were applied: a chain of beads (pearl necklace model) and a more refined so-called San necklac e model. Using the San necklace model, the relaxation time was found t o be in the range of 9 to 18 mu s (depending on the flexibility of the joint), which is in accordance with what has been obtained from intri nsic viscosity measurements, but considerably higher than experimental data from measurements of transient electric birefringence.