Turnover of Nitrate Reductase in Neurospora crassa

Abstract

<p>Turnover of nitrate reductase in Neurospora crassa was examined in mycelia incubated in varying conditions. This study showed that the specific activity of the enzyme was very dependent on the age of the mycelia: it was highest in young mycelia which were in an exponential stage of growth. Both the rate of induction and the rate of decay in vivo and in cell-free extract were also highest in the mycelia in logarithmic growth phase. Comparison of the rate of induction and decay of nitrate reductase in exponentially growing mycelia on nitrate media and on media with no nitrogen suggested that the higher specific activity of the enzyme on nitrate media was perhaps a result of the protective effect of nitrate on the enzyme. The rate of decay of nitrate reductase in mycelia on ammonia media incubated at different ages and different temperatures was markedly different from the rate of decay of the enzyme in similarly treated mycelia on nitrate or no nitrogen media. This suggested that there might be two different mechanisms of decay.</p> <p>An assay was developed to examine protease levels of the mycelia incubated in varying conditions. There was little evidence for the involvement of a protease in the decay of nitrate reductase, but the pattern of decay of the enzyme is consistent with the hypothesis that a protease may act as the mechanism of decay.</p>