Glutamate
Vegemite, like many foods including tomatoes, cheese, mushrooms and meat, contains unrefined glutamate[1], not to be mistaken with Mono-sodium Glutamate (MSG) -- a salt-bound, chemically-refined form of this flavour-enhancing natural amino acid. Vegemite contains 1.4% of unbound, natural glutamate amino acid, and an unknown quantity of the bound form, which also occurs naturally in many common foods.
From some site caled wiki cookbooks or something. But all the info is about 50/50 so I couldn't say for sure, it does have a lot of salt though