The Hexokinases from Wild‐Type and Morphological Mutant Strains of Neurospora crassa

Four hexose‐phosphorylating isozymes (hexokinases α, β, γ and δ) were separated by DEAE‐ cellulose column chromatography of high‐speed supernatants from Neurospora crassa wild‐type strains 77a and RL3‐8A. The isozymes displayed broad sugar specificity and Michaelis constants for glucose in the micromolar range. The isozymes were not inhibited by glucose 6‐phosphate nor activated by citrate. Molecular weights were estimated as 95 000 by gel filtration. Glucose‐specific kinases were not found. Marked quantitative variations in the relative proportion of the hexokinases were observed during growth of the fungus on minimal medium plus sucrose. Hexokinase p was the predominant form (82% of the total activity) during the period of hyphal growth. At maturation time all the isozymes were present at about the same level although a small preponderance of hexokinase β was still evident. The relative proportions of the hexokinases did not vary when sucrose was replaced by glucose, fructose or casamino acids. When sorbose was added to the minimal medium containing sucrose, a high proportion of hexokinase β was apparent concomitantly with the well known change of growth to a colonial mode. Several morphological mutant strains were examined with respect to the hexokinase profile. Strains COI‐16 and crisp showed a marked preponderance of hexokinase β. Extracts from the dapple and dingy strains lacked hexokinases a and δ. Rabbit antisera to commercial preparations of hexokinase PI and PII from Saccharomyces cerevisiae were able to inhibit partially the enzyme activity of Neurospora hexokinases γ and δ. No effect of the antisera on hexokinases a and B could be observed.