hematin vs protoheme

hematin and protoheme both are nouns.

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

As nouns, hematin and protoheme are synonyms defined as:

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

Other synonyms of hematin include haem, haemitin, heme.

hematin (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