haem vs protoheme

haem and protoheme both are nouns.

Word	Noun	Adjective	Verb	Adverb
haem	Yes	No	No	No
protoheme	Yes	No	No	No

As nouns, haem and protoheme are synonyms defined as:

haem and protoheme: a complex red organic pigment containing iron and other atoms to which oxygen binds

Other synonyms of haem include haemitin, hematin, heme.

haem (noun)	protoheme (noun)
a complex red organic pigment containing iron and other atoms to which oxygen binds	a complex red organic pigment containing iron and other atoms to which oxygen binds