Turns up, source of illumination about first race is produced as publicity for the bookmaker (5)
I believe the answer is:
blurb
'produced as publicity for the bookmaker' is the definition.
I can't judge whether this defines the answer.
'turns up source of illumination about first race' is the wordplay.
'turns up' says the letters should be written in reverse.
'source of illumination' becomes 'bulb' (bulb is a kind of source of illumination).
'about' is an insertion indicator.
'first' says to take the initial letters.
The initial letter of 'race' is 'r'.
'bulb' enclosing 'r' is 'brulb'.
'brulb' backwards is 'BLURB'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for blurb that I've seen before include "Publisher's puff" , "Publisher's descrtion of book" , "words on jacket?" , "Publisher's text on book" , "Promotional statement, on book-cover say" .)