Complex sentence: Cross-linking methods developed prior to PICUP, including the use of physical, oxidative, and chemical cross-linkers, often require more time and results in protein byproducts and the cross-linked protein yield is very low due to the multifunctionality of the cross-linking reagents.
Split into simpler sentences: Cross-linking methods developed prior to PICUP, including the use of physical, oxidative, and chemical cross-linkers, often require more time and result in protein byproducts. In addition, the cross-linked protein yield is very low due to the multifunctionality of the cross-linking reagents.