Jean Botts

Use of Fluorescence Polarization to Observe Changes in Attitude of S-1 Moieties in Muscle Fibers

The fluorophore, N(iodoacetylamino)-1-naphthylamine-5-sulfonic acid (1,5-IAEDANS), incubated with glycerinated psoas fibers primarily labels the S-1 moieties of such fibers, but it does not impair fiber contractility even when the degree of labeling is as high as 0.8 moles fluorophore per mole myosin. The polarization of the on-axis fluorescence from either the IAEDANS fluorophore, or the intrinsic tryptophane fluorophore, depends on whether the fiber is relaxed, in rigor, or developing isometric tension; furthermore, the changes in polarization on going from one state to another are much the same with either tryptophane or IAEDANS fluorophores. The foregoing is true whether the plane of the exciting light is parallel or perpendicular to the fiber axis. Also, if a fiber is first freed of its myosin by extraction, and is then incubated with IAEDANS-labeled S-1 the resulting polarization approaches that observed with a labeled, unextracted fiber in rigor. By contrast, incubation with the fluorophore, 7-nitro-4-chlorobenz-2-oxa-1,3-diazole (NBD-Cl) confers fluorescence only on actin, without impairing contractility, but the polarization of such fluorescence changes in a different direction and magnitude from myosin-originating fluorescence. It is concluded from these various observations that whether the fluorophore is IAEDANS or tryptophane the polarization change with change in physiological state originates in the S-1 moieties of fibers, and relates to the space attitude of these moieties.

A model for the elementary process in muscle action.

Abstract Evidence is adduced in favor of the following theory for the elementary process in muscle action: In the “resting state” the lengths of the molecular filaments in “myosin” are a compromise between the contracting tendency of intramolecular Brownian movement and the extending tendency of a net charge repulsion. This net charge is positive, due to the adsorption of bivalent cations. The anion of adenosine triphosphate (ATP) adsorbs on the “myosin,” discharging it, thus reducing or abolishing the repulsion; the filaments then contract, gaining configurational entropy. Enzymatic dephosphorylation eventually converts ATP to adenosine diphosphate, which is not strongly adsorbed. By this process, negative charge is eventually removed, and the repulsion due to the resulting net positive charge re-extends the filaments.

Approximate Configurational Partition Functions for Certain Aggregates of Spherical Molecules

There are calculated by two different methods the number of ways in which i sites out of a total of n sites may be filled in such a manner that among the filled sites there will be p nearest neighbor pairs when the sites form certain regular spherical surface lattices: the contact points on any sphere in the cubic and hexagonal closest packings of spheres, and in the simple cubic packing of spheres. The use of these results in the treatment of a model of antibody‐antigen combination is briefly indicated.