Some physical properties of purified fraction I protein from spinach chloroplasts

Pon, N.G.

Archives of Biochemistry and Biophysics 119(1): 179-193


ISSN/ISBN: 0003-9861
PMID: 6052416
Accession: 025493366

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Fraction 1 protein, from spinach chloroplasts and homogeneous by electrophoretic and sedimentation velocity criteria, had, an uncorrected specific refractive increment of 1.69 X 10-4 ml/mg protein at 10.0° and 546 mμ. Its specific extinction coefficient was 1.82 at 1 mg/ml in pH 8.0, 0.001 Tris-chloride for a 1-cm light path. Moving boundary electrophoresis of this protein at about 4 ° yielded mobilities from -3.2 to 6.2 X 10-5 cm2 volt-1 sec-1 at pH 6.3-9.5, which, on extrapolation, indicated an isoelectric point around pH 4.3-5.5. The sedimentation coefficient decreased with increasing protein concentration above 0.3 mg/ml and was 18.7S when extrapolated to zero concentration. At less than 0.3 mg/ml, the sedimentation coefficient decreased with decreasing concentration, suggesting the dissociation of the protein. The apparent diffusion coefficient was 3.01 X 10-7 cm2 sec-1, which when combined with the extrapolated sedimentation coefficient gave a molecular weight of 559,000. Sedimentation equilibrium experiments gave a limiting molecular weight at the meniscus of 475,000 + 11,000 and suggested the presence of a 545,000 molecular weight component. An attempt was made to explain the 17% discrepancy between the molecular weights from sedimentation velocity runs and that from sedimentation equilibrium runs.