Abstract
The uptake of putrescine, spermidine and spermine was studied in Aspergillus nidulans using 14C-labelled polyamines. Active transport systems, inhibited by azide and regulated by nitrogen availability, exist at least for putrescine and spermidine. Putrescine is taken up two to three times more rapidly than spermidine, reflecting a lower Km for the former substrate. The two uptake systems appear to be independent, spermidine uptake being inhibited by both putrescine and spermine, while putrescine uptake is not inhibited by the other two polyamines. The relationships of these transport systems to the tenfold or greater difference between spermidine and putrescine concentrations required to support growth of the putrescine auxotroph are discussed.
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