An outer metabolic region of the yeast cell

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Abstract
The theoretical interspace for a large number of non-deformable spheres with close packing is 26% of the total vol. Centrifuged yeast (3000 rpm. for 20 min.) shows an interspace vol. of 23% with inulin as the test substance, 22% with gelatin and 24% with peptone, when expressed as a percentage of the total vol. The interspace fluid can be pressed out with simple hand press, so that an amt. representing only 0-5% of the total cell volume is left. If the space be measured with arabinose, galactose, or lactose, with allowance for the water abstracted from the cells, it appears as 33-34%. The difference is due to the penetration of such substances into an outer cell region which is identified with the thick cell wall. The water for soln. in this outer region is 0.10-0.11 of the total cell vol. Into this part of the cell many substances penetrate readily, including NaCl and KCl; also succinic acid, glyceric acid, etc. but succinate ions are debarred or enter slowly. The inner surface or membrane of the outer region is impermeable to chloride ions in the resting yeast. It is likewise impermeable or only very slowly permeable to succinic acid, glyceric acid\and a number of other acids with hydroxyl or amino groups. On the other hand, it is very freely permeable to formic, acetic, propionic and butyric acids.
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