Trace metal requirements and some enzyme systems in a riboflavin-requiring mutant of Neurospora crassa.

Abstract

SUMMARY: A mutant of Neurospora crassa is shown to have an absolute requirement for riboflavin when grown at 30°, but this requirement is less stringent when the organism is grown at 25°. The Fe, Cu, Zn, Mn and Mo requirements of the mutant, grown at either temperature, are similar to those of the wild type (146) so that it seems unlikely that these metals are involved in the biosynthesis of riboflavin. A study of enzyme patterns in the mutant, grown at 30° and given optimal or deficient concentrations of riboflavin, demonstrated alternative pathways of electron transfer in the fungus. When riboflavin is deficient, the iron enzymes are markedly increased and oxygen is probably the main terminal acceptor of the electrons. At optimal concentrations of riboflavin, the flavoprotein enzymes are produced and nitrate and nitrite reductases are active so that nitrate can act as a terminal acceptor. Iron deficiency is readily produced in the mutant when riboflavin is deficient because of the increased activity of iron enzymes; a molybdenum requirement is greater at optimal riboflavin concentrations because of the enhanced production of molybdo-flavoproteins.