Molecular weights of the slow and fast forms of T2L bacteriophages

Abstract

' calculated the molecular weights of the "slow" and "fast" forms of the bacteriophage T2L by applying the Svedberg relation between the sedimentation and diffusion coefficients. They used a diffusion coefficient determined by quasielastic light scattering techniques and found that the calculated molecular weight of the "fast" form (tail fibers folded back) was 1.22 times that of the "slow" form (tail fibers stretched). They attributed this anomalous result to thermodynamic or hydrodynamic nonideality.It is possible however to explain the anomaly in another way. It is doubtful whether the application of standard formulas to the results of quasielastic light scattering yields the correct translational diffusion coefficient in the case of lollipop-shaped particles like the T-even bacteriophages. Such particles consist of an ellipsoidal head and a rodlike tail. As almost all the mass of such particles is packed in the head, we assume that the light is scattered by the head only. The hydrodynamic center of the particles is positioned a t a distance ro from the center of the head towards the tail. Recently we calculated2 the correlation function of the light scattered by lollipop-shaped particles, taking into account not only the distance ro, but also the optical anisotropy and the nonzero dimensions of the head. In the case of T-even phages, the latter two factors may, however, be neglected to a first approximation.It can be shown2 that the first-order correlation function of the field scattered from lollipop-shaped particles can be written as( 1) where ro is the distance between the hydrodynamic and scattering centers, q is the magnitude of the scattering vector, DT is the translational diffusion coefficient, DR is the rotational diffusion coefficient, and Bf are coefficients depending on the product qro (and in principle also on the anisotropy and dimensions of the particles). I=OThis correlation function can be characterized by Koppel's method3 of cumulants as -where A = x&.

Quasielastic light scattering from solutions of lollipop‐shaped particles

“…(6) in terms of spherical harmonics Ylrn(Q). In order to get rid of normalization factors, we define (8) First we calculate a(Q). It is given by the yy element of the polarizability tensor of a particle with orientation Q (Fig.…”

“…Rotational diffusion will then give rise to phase fluctuations of the light scattered by a particle in addition to the phase fluctuations caused by = DTq2, where q is the scattering vect0r.l Biopolymers, Vol. 18,1533-1542(1979 0 1979 John Wiley & Sons, Inc.…”