Is it ensure, insure, or assure?
scleroprotein scle·ro·pro·tein (sklēr'ō-prō'tēn', -tē-ĭn)
Any of a class of generally insoluble proteins found in skeletal and connective tissue. Also called albuminoid.
any of several fibrous proteins of cells and tissues once thought to be insoluble but now known to be dissolved by dilute solutions of acids such as citric and acetic