Amino acid transport in Neurospora crassa III. Acidic amino acid transport

Kinetic studies of uptake demonstrate the existence of an active transport system for d - and l -acidic amino acids in Neurospora crassa. This system, designated amino acid Transport System IV, has K m ' s for l -cysteic, l -aspartic and l -glutamic acids of 7, 13 and 16 μM, respectively. It has higher affinity for d -aspartic acid than for l -aspartic acid but lower affinity for d -glutamic than for l -glutamic acid. Transport System IV has low activity in growing mycelial pads but has higher activity in carbon-, nitrogen- or sulfur-starved pads. The characterization of Transport System IV appears to complete the outlining of the major amino acid transport systems in Neurospora. A comparison is made among the substrate affinities and regulation of several amino transport systems in Neurospora and in two other fungi.