Regulation by Glutamine of Ammonia Transport in Aspergillus nidulans

Abstract

Summary: Conidia of Aspergillus nidulans had a very low activity of a high affinity ammonia transport system. During germination the activity increased, reaching a maximum soon after the onset of exponential growth. The activity in germinated conidia varied with the nitrogen source in the germination medium. Analyses of intracellular ammonia and amino acids revealed that a low level of ammonia transport activity was associated with a high intracellular concentration of glutamine and vice versa. The intracellular concentration of glutamine is probably involved in repression of synthesis of the ammonia transport system. It is suggested that glutamine and asparagine (rather than ammonia itself) regulate the pre-formed ammonia transport system by inhibition from within the intracellular pool. It is concluded that glutamine and glutamine synthetase may be more important in the regulation of some aspects of nitrogen metabolism rather than ammonia and glutamate dehydrogenase as has been previously suggested.