No abstract

In order to characterize the several isoenzymes of soybeans, they were examined with respect to the effect of the polar nature of the substrate. In general, lipoxygenase‐1 was most active when presented with charged substrates such as the anionic form of linoleic acid or of potassium linoleyl sulfate, whereas lipoxygenase‐2 and‐3 preferred nonpolar substrates such as unionized linoleic acid, methyl linoleate, linoleyl methane sulfonate, 10,13‐nonadecadieneamine, or linoleyl acetate. Linoleyl sulfate, which has been advanced as an excellent readily soluble substrate for lipoxygenase, was indeed the best substrate found for lipoxygenase‐1. Lipoxygenase‐2 and‐3 were, by contrast, totally inactive against this substrate. The favorable response of linnoleic acid to lipoxygenase‐2 and‐3 at pH 6.8 was ascribed to the anomalously high pKa value of linoleic acid compared to that of short chain carboxylic acids. The pH‐activity profile obtained with lipoxygenase acting on linoleyl sulfate (which was charged at all pH values examined) was shifted to lower pH values compared to the linoleic acid activity profile. The effect of changing from the charged to the uncharged substrate, when tested against lipoxygenase‐1, was to increase the Km by an order of magnitude.

No abstract

A mucilaginous matrix produced by the fungus Colletotrichum graminicola has several properties which enhance survival of fungal spores. The purpose of this research was to resolve and characterize the compounds of the matrix to facilitate investigation of their function. The major component is a group of high molecular weight glycoproteins composed of oxygen-linked oligomers of rhamnose and mannose and high levels of hydrophobic and hydroxylic amino acids. The amino acid composition and percentage carbohydrate of this viscous material are similar to that of mucins, which may account for the antidesiccant property of the matrix. In addition to the previously reported invertase and esterase, a specific pglucosidase was identified as a matrix component. Three nonprotein, UV-absorbing components were resolved from the matrix; one of these was identified as uracil.The anthracnose disease of corn and sorghum is a limiting factor in the production of these crops in the developing nations of the humid and semiarid tropics