Abstract: A series of photogelatin samples extracted for different times was collected, The reducing power (RP) was determined by potential titration method, the Methionine, Metsox and Metson contents were evaluated with L-8500 amino acid analyzer, the molecular weight distribution of the different conformation components contained in different extracts (No.1-5) was found with SDS-PAGE method.It was shown that a maximum was found on the curve of RP versus extraction depth and a parallel relationship was demonstrated between RP and the α₁, α₁ + α₂ or α₁/α₂.This parallel relationship can be elucidated by the following 2 main points: (1) α₁ chain contains higher content of Met than that of α₂ chain, which can be clearly seen from their primary structure of amino acid sequence; (2) among the extracted gelatings (No.1-5)only the gelatin of the 2nd extract ranks the 1st containing the highest content of α₁ conformation component.The discovery and the elucidation of the parallel relationship between RP and extraction depth are of significance in the classification and specification of photogelatins and in making full and reasonable use of different gelatin-extracts in various specified circumstances.

Key words: gelatin, extraction, conformation, reducing power