Self‐assembly and cross‐linking of Volvox extracellular matrix glycoproteins are specifically inhibited by Ellman's reagent

A major impediment to the biochemical characterization of extracellular matrices from algae (as well as higher plants) is the extensive covalent cross‐linking that exists in the matrix, rendering most components insoluble and resistant to conventional extraction procedures. In the multicellular green alga Volvox , biogenesis of the extracellular matrix (ECM) is initiated immediately after the process of embryonic inversion. At this stage of development, the sulfhydryl reagent 5,5′‐dithio‐bis(2‐nitrobenzoic acid), known as Ellman's reagent, interferes in a highly specific manner with ECM biogenesis. Treated post‐inversion embryos are no longer able to assemble an intact ECM and consequently dissociate into a suspension of single cells. Dissociated cells remain viable and continue to secrete ECM proteins into the growth medium, as documented by the identification of several members of the pherophorin family. Cross‐linked ECM polymers such as sulfated surface glycoprotein 185 remain in a soluble state. Thus, treatment with Ellman's reagent opens a simple approach for the isolation and characterization of otherwise inaccessible monomeric precursors.