13321
The observation of D - spacing distribution by self - assembly of type I collagen alone is significant as it eliminates the necessity to invoke other preassembly or postassembly hypotheses , such as variation in the content of collagen types , enzymatic cross - linking , or other post - translational modifications , as mechanistic origins of D - spacing distribution .
 None
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities:  
Answer:
 None