heme vs protoheme

heme and protoheme both are nouns.

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

As nouns, heme and protoheme are synonyms defined as:

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

Other synonyms of heme include haem, haemitin, hematin.

heme (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