SUMMARY: Potassium and C-labelled proline, aspartic acid, glutamic acid, and alanine were accumulated by , during glucose oxidation, over a range of water activity ( ) values. In the absence of amino acids, potassium accumulation increased to a maximum as was decreased to about 0·975 but then dropped to a low value at 0·960 ; with an amino acid, potassium accumulation was much increased and maximum uptake occurred at 0·960 [C]Proline uptake increased linearly with decrease in , the accumulated proline being metabolized in part to glutamic acid and to deaminated compounds; at 0·95 uptake of [C]-proline reached 1·4 mmol/g dry bacteria. Uptake of aspartate was comparable to that of proline at down to 0·98 but then decreased. Relatively little exo-genously supplied glutamate or alanine was accumulated at any water activity. At levels below 0·98, oxygen uptake by non-growing bacterial suspensions increased with time and accompanied the linear uptake of proline. Proline accumulation ceased when a maximum rate of oxygen consumption was reached. At 0·97 the rate of proline uptake was unaffected by a mixture of 19 amino acids, but the total proline uptake decreased to one-half. In contrast, the proline homologue azetidine-2-carboxylic acid lowered the rate and extent of proline accumulation by one-third.


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