11739
The accepted proton pumping stoichiometry was 4 protons per 2 electrons transferred ( 4H ( + ) / 2e ( - ) ) but it has been suggested that stoichiometry may be 3H ( + ) / 2e ( - ) based on the identification of only 3 proton pumping units in the crystal structure and a revision of the previous experimental data .
 Chemical: 4H ( + ); Chemical: 3H ( + )
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: 4H ( + ); Chemical: 3H ( + )