Indoxyl

Abstract: A technique for the histochemical demonstration of non-specific alkaline phosphatase was developed using a medium containing indoxyl phosphate and a tetrazolium salt, Nitro B.T. The tetrazolium salt was reduced to diformazan by the hydrogen ions released by the formation of either indigo or indigo white by reaction of the enzyme on the indoxyl phosphate. The localization in the organs investigated was similar to that obtained by the standard azo dye and lead techniques.

Abstract: A NEW diazonium salt, ‘hexazonium pararosanilin’, introduced for simultaneous azocoupling methods by Davis and Ornstein1, was successfully employed in the demonstration of esterases at microscopic and electron-microscopic levels2,3. It was found that a method using α-naphthyl phosphate and hexazonium pararosanilin as coupler gives far better localization of acid phosphatase than any other method4 using the same substrate, and the results seem to be not inferior to techniques using ‘Naphthol AS’5 or indoxyl phosphates6. The advantages of this method, besides the very good localization, are that α-naphthyl phosphate is water-soluble; it is more readily hydrolysed than the phosphate esters of ‘Naphthol AS’, or indoxyl derivatives, the reagents are commercially available, and the method works easily.

Abstract: Indigo is an ancient dye uniquely capable of producing the signature tones in blue denim; however, the dyeing process requires chemical steps that are environmentally damaging. We describe a sustainable dyeing strategy that not only circumvents the use of toxic reagents for indigo chemical synthesis but also removes the need for a reducing agent for dye solubilization. This strategy utilizes a glucose moiety as a biochemical protecting group to stabilize the reactive indigo precursor indoxyl to form indican, preventing spontaneous oxidation to crystalline indigo during microbial fermentation. Application of a β-glucosidase removes the protecting group from indican, resulting in indigo crystal formation in the cotton fibers. We identified the gene coding for the glucosyltransferase PtUGT1 from the indigo plant Polygonum tinctorium and solved the structure of PtUGT1. Heterologous expression of PtUGT1 in Escherichia coli supported high indican conversion, and biosynthesized indican was used to dye cotton swatches and a garment.