import re
strings = [
">Keratyna 5, egzon 2, Homo sapiens",
">101m_A mol:protein length:154 MYOGLOBIN"
]
for s in strings:
print(re.split(r", | (?!.*?, )", s, maxsplit=1))
aW1wb3J0IHJlCgpzdHJpbmdzID0gWwogICAgIj5LZXJhdHluYSA1LCBlZ3pvbiAyLCBIb21vIHNhcGllbnMiLAogICAgIj4xMDFtX0EgbW9sOnByb3RlaW4gbGVuZ3RoOjE1NCAgTVlPR0xPQklOIgpdCgpmb3IgcyBpbiBzdHJpbmdzOgogICAgcHJpbnQocmUuc3BsaXQociIsIHwgKD8hLio/LCApIiwgcywgbWF4c3BsaXQ9MSkp