Part I: Synthesis of L-Amino Acid Oxidase by a Serine- or Glycine-RequiringStrain of Neurospora
Wild-type cultures of Neurospora crassa growing on minimalmedium contain low levels of L-amino acid oxidase, tyrosinase, andnicotinarnide adenine dinucleotide glycohydrase (NADase). The enzymesare derepressed by starvation and by a number of other conditions whichare inhibitory to growth. L-amino acid oxidase is, in addition, inducedby growth on amino acids. A mutant which produces large quantities ofboth L-amino acid oxidase and NADase when growing on minimal medium wasinvestigated. Constitutive synthesis of L-amino acid oxidase was shownto be inherited as a single gene, called P110, which is separable fromconstitutive synthesis of NADase. P110 maps near the centromere onlinkage group IV.
L-amino acid oxidase produced constitutively by P110 was partiallypurified and compared to partially purified L-amino acid oxidaseproduced by derepressed wild-type cultures. The enzymes are identicalwith respect to thermostability and molecular weight as judged by gelfiltration.
The mutant P110 was shown to be an incompletely blocked auxotrophwhich requires serine or glycine. None of the enzymes involvedin the synthesis of serine from 3-phosphoglyceric acid or glyceric acidwas found to be deficient in the mutant, however. An investigation ofthe free intracellular amino acid pools of P110 indicated that themutant is deficient in serine, glycine, and alanine, and accumulatesthreonine and homoserine.
The relationship between the amino acid requirement of P110 andits synthesis of L-amino acid oxidase is discussed.
Part II: Studies Concerning Multiple Electrophoretic Forms of Tyrosinasein Neurospora
Supernumerary bands shown by some crude tyrosinase preparationsin paper electrophoresis were investigated. Genetic analysis indicatedthat the location of the extra bands is determined by the particular Tallele present. The presence of supernumerary bands varies with themethod used to derepress tyrosinase production, and with the durationof derepression. The extra bands are unstable and may convert to themajor electrophoretic band, suggesting that they result from modificationof a single protein. Attempts to isolate the supernumerary bandsby continuous flow paper electrophoresis or density gradient zonalelectrophoresis were unsuccessful.
