Dear fellow researches,

I stumbled upon a text passage in which the change in absorbance upon binding of DMMB to GAG (glycosaminoglycans) was described as a metachromatic effect:

"The dye 1,9-dimethylmethylene is a thiazine chromotrope agent that presents a change in the absorption spectrum due to the induction of metachromasia when bound to sulfated GAGs enabling rapid detection of GAGs in solution (Whitley et al., 1989; Chandrasekhar et al., 1987; Farndale et al., 1982)"

However, I always thought that changes in the absorption spectrum were shifts of wavelength that could be described as bathochromic (shift to shorter wavelength), hypsochromic (shift to longer wavelength). Whereas metachromatic changes are described as the colour changing of some sort of biological tissue upon exposure to a differently coloured dye. For example if a blue dye turns structures in a tissue purple. So, in short...I do not think that the term 'metachromasia' applies to the DMMB-GAG assay. Or does it?

Can somebody help to clarify this? Possibly with references?

That would be really helpful.