 A follow-up paper was written in 1937 that referenced other researchers on hydrogen bonding in proteins, such as Maurice Loyal Huggins and Linus Pauling.Wrinch also wrote a paper with William Astbury, noting the possibility of a keto-enol isomerization of the >CαHα and an amide carbonyl group >C=O, producing a crosslink >Cα-C(OHα)< and again converting the oxygen to a hydroxyl group.Such reactions could yield five-membered rings, whereas the classic cyclol hypothesis produces six-membered rings.