protoheme vs heme

protoheme and heme both are nouns.

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

As nouns, protoheme and heme are synonyms defined as:

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

Other synonyms of protoheme include haem, haemitin, hematin.

protoheme (noun)	heme (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