Which word in this sentence is the longest?

see this link to see the longest Word in the world. Word-has-189819-letters-takes-three-hours-to-pronounce/">https://www.digitalspy.com/fun/a444700/longest-Word-has-189819-letters-takes-three-hours-to-pronounce/ 'Methionylthreonylthreonylglutaminylarginyl...isoleucine' is the chemical name of 'titin' (also known as 'connectin') - the largest known protein. It has 189,819 letters.