AMINO ACID TRANSPORT IN MICROORGANISMS 583 
affected should not be penetrated by sucrose. To determine the magnitude of this 
space the distribution of sucrose in pellets of normal and vitamin B,-deficient cells 
was measured. The results expressed as impermeable volumes are summarized in 
Table IV. The sucrose-impermeable volume is only slightly lower than the total cell 
volume (the difference between total pellet volume and extracellular space measured 
by dextran and inulin). In pellets of B,-deficient cells the slightly larger difference 
between these values may be due partly to the presence of a small population of 
dead, completely permeable cells and possibly to a more porous cell wall which 
TABLE IV 
PERMEABILITY OF L. avabinosus TO SUCROSE* 


HB, cells LB, cells 
Space measured Test substance —<——— ——— = 
Volume (ml/g dry wt.) 
Total pellet — 4.16 4.43 
Total cell Dextran 3.15 3.13 
Total cell Tnulin 3.04 3.19 
Sucrose impermeable Sucrose 2.87 2.58 
Sucrose impermeable (44C|Sucrose 2.43 2.23 

at 37° for 45 min in an equal volume of the test substance dissolved in 0.12 MW 
phosphate buffer. Dextran (avg. M. W. 60 000-go 000) was used at 100 mg/ml, 
inulin at 50 mg/ml, and sucrose at 0.2 or 0.3 M. The cells were centrifuged and the 
supernatant analyzed as follows: dextran by the anthrone method’, inulin by the 
anthrone and Ror methods®, and sucrose by radioactivity or the Ror method. 
The values shown are averages of 4 experiments with each cell type. 
admits a greater amount of sucrose relative to inulin or dextran than occurs in control 
cells. It is clear that at least 75°%, and possibly much more, of the cell interior is not 
penetrated by sucrose, suggesting strongly that sucrose is excluded from that part 
of the cell lying within the surface membrane, and, therefore, that it must increase 
accumulation by preventing water influx into this region of the cell. These data, 
however, give no certain information whether water influx is deleterious to accumula- 
tion because the membrane is distended or because intracellular structures are 
disrupted. 
These findings could be interpreted with greater confidence if a procedure was 
available which could reduce membrane distention without influencing movement of 
water into the protoplast. The finding that the cell wall of vitamin B,-deficient cells 
is defective and that conditions which permit deposition of additional cell wall 
material also restore normal accumulation activity appeared to satisfy these require- 
ments. Electron microscopic examination has shown that B,-deficient cells of 
L. arabinosus contain a much thinner than normal cell wall layer external to the mem- 
brane (Fig. 8)**°. Deficient cells also yield only one-half the amount of cell wall 
* The occurrence of complex intracellular membranous structures appearing as extensions of 
the cytoplasmic membrane (as shown in Fig. 8A) indicates the shortcomings of the simple view 
that the bacterial cell consists of a largely disorganized cytoplasm contained within a sack (the 
cytoplasmic membrane). Earlier speculative suggestions that accumulation phenomena in micro- 
organisms might involve interactions with intracellular membranes must now be given more 
serious attention especially in attempting explanations for pool heterogeneity. 
References p. 592/594 
