Abstract: Provided is a pretreatment method for structural analysis of a protein, including chemical modifying and fragmenting a protein to be analyzed, in which in the fragmenting, the protein is treated at a temperature of 60 to 99° C. in the presence of a heat-resistant protease that has four or more cleavage sites and is soluble or immobilized on a carrier.

Abstract: Objects of the disclosure are to provide a preanalysis treatment method for a sample, which can reduce mixing of a reagent into the sample, and to provide a sample pretreatment system capable of performing the preanalysis treatment method. An aspect of the present embodiment is a preanalysis treatment method for a sample, which includes a step A of mixing the sample and a reagent A containing a support and a reducing agent immobilized on the support, a step B of mixing the sample and a reagent B containing a support and an enzyme immobilized on the support, a step X-A of, after the step A, separating the reagent A and a supernatant from each other, and a step X-B of, after the step B, separating the reagent B and a supernatant from each other.