12248
Mass spectra showed that the P - N bonds were stable during trypsin digestion at pH 8 but were cleaved during pepsin digestion at pH 2 .
 Chemical: P - N
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: P - N