protoheme vs haem

protoheme and haem both are nouns.

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

As nouns, protoheme and haem are synonyms defined as:

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

Other synonyms of protoheme include haemitin, hematin, heme.

protoheme (noun)	haem (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