Abstract
A transport double mutant of Neurospora crassa has been shown to retain only the three transport systems capable of L-histidine uptake. The substrate specificity of the remaining transport system, termed the general transport system, has been fully characterized with regard to the contributions to binding of the side chain, the α-amino group, and the carboxylate group. The positively charged α-amino groups is necessary for binding; the negatively charged carboxylate group is of less importance, since its replacement by a neutral carbonyl functional group does not completely abolish binding. The greatest structural latitude for binding was found in the side chain; affinity for α-amino acids was uniformly high except for L-aspartic and L-glutamic acid, L-asparagine, and L-proline. Thus, this transport system is "general" with these restrictions. Two potential affinity labels for amino acids transport systems in Neurospora crassa have been studied. Exogenous L-leucine chloromethyl ketone (LUCK, 3-amino-1-chloro-5-methyl-2-hexanone) inactivates the general and the neutral amino acid transport systems, activates the basic amino acid transport system, and only weakly inactivates the D-glucose transport system. The only significant effect of exogenous L-lysine chloromethyl ketone (LCK, 3,7-diamino-1-chloro-2-heptanone) was activation of the general amino acid transport system. Iodoacetamide and sodium iodoacetate rapidly inactivate all four systems. Although specificity in the action of LUCK is demonstrated, since natural amino acid substrates for the general and neutral amino acid transports systems do not prevent or reduce inactivation of these systems. ...
Nelson, Stephen Ozro (1974). Transport in Neurospora crassa: specificity of the general amino acid transport system and effects of alkylators, sulfhydryl reagents, and metabolic inhibitors on amino acid and D-glucose transport. Doctoral dissertation, Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -172542.