OSMOTIC PRESSURE DETERMINATIONS WITH ISOLATED PROTOPLASMIC PROTEINS

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Abstract
Slices of potato tubers were freeze-dried, ground in a Wiley mill, extracted with phosphate, and the extract precipitated with (NH4)2SO4. The pH was maintained at 7 to 7.6. The precipitate was filtered off and transferred to a collodion micro-cup of 0.2 ml. capacity. The microcup was attached to an adjustable mercury manometer and the protein dialysed for 24 hrs., after which the pressure was read. Curves of pressure vs. conc. enabled detns. of mol. wt. and relative hydra -tion. The average mol. wt. was about 40,000-50,000. The curves for proteins from active tissues rose more steeply than those for proteins from dormant tissues, due to smaller molecular weight or greater hydration. Proteins were synthesized in considerable quantity when the tubers were transferred from 0[degree]C to 25[degree]C for about a week.