Effects of Mammalian Insulin on Metabolism, Growth, and Morphology of a Wall-Less Strain ofNeurospora crassa*

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Abstract
Addition of mammalian insulin to a nutritionally rich, chemically defined culture medium affects Neurospora crassa "slime" (wall-less) cells, as indicated by enhancement of growth, extension of viability at the stationary phase of growth, alteration of morphology, and stimulation of glucose oxidation. Bovine, porcine, and recombinant human insulin had similar effects on growth and morphology, while proinsulin, reduced insulin, and several other proteins were inactive. Insulin added in the presence of excess antiinsulin antibody was without activity. Intact cells possessed high affinity insulin-binding sites, represented by a curvilinear Scatchard plot, suggesting that effects are mediated through insulin receptors on the cell surface. These findings establish a role for insulin or insulin-like molecules in regulating growth and metabolism in this fungal cell and demonstrate a close similarity to insulin effects on certain mammalian cells.