STUDIES ON SILK FIBROIN. II. SEDIMENTATION COEFFICIENT DISTRIBUTION OF FIBROINS

1 The sedimentation coefficient distributions of silk fibroin samples prepared by extraction of silk fibre by boiling Na2CO3 solution for different intervals of time were determined. 2 Samples from 150 and 180 min extraction gave sharper distribution curves than those from 30, 60, 90 and 120 min extraction. 3 The s2corr vs (t — t0) plots for samples from 30, 60, 90 and 120 min extraction showed upward curvature indicating heterogeneity of the preparation. On the other hand, samples from 150 and 180 min extraction gave linear plots. 4 The molecular weight of the sample from 180 min extraction was calculated from the sedimentation coefficient and the diffusion coefficient obtained from the linear s2 vs (t — t0) plot. This value was in good agreement with the limiting value obtained at higher speeds of centrifugation by the Archibald method. However, it was lower than the molecular weight determined by the Archibald method at low speeds, indicating the heterogeneous nature of this sample also.