"Fractions of the wallet" - yes. "Fractions of a key" - no. Keys (and their associated balances) are transferred altogether, so you cannot transfer less than a key (that would effectively mean you are sharing it with someone else and the whole point is to make sure the key is only held by a single person at any given time). If you need to "break" a key into smaller amounts, you can easily do so through the Bitcoin network - transfer the key you want to split to the Bitcoin wallet, then fund two (or more) OtherCoin addresses from it with any values you need. This is also how you can pay the exact amount requested = you pay the majority in OtherCoin, then if the merchant wants to receive _exactly_ what he's asked for, you either pay the rest via Bitcoin or you break an OtherCoin key into two smaller ones, then transfer one to the merchant (for the remaining amount to pay).