Milliyet's Semih Idiz takes a look at this question in a column (translated into English in today's Hurriyet Daily News). From his column:
Iran, it seems, is going to turn into one of the main litmus tests of exactly how influential Turkey has become in the region.
Ankara is in an uncomfortable position in this respect. If it does not manage to bring Tehran around to a reasonable position on the uranium-enrichment issue, it runs the risk of being isolated among its allies.
On the other hand, if Iran decides to listen to Turkish Foreign Minister Ahmet Davutoğlu when he visits Tehran to discuss this matter over the next days, it will be a major coup for him and his “proactive foreign policy.” Few, however, are expecting a major breakthrough.
Iranian President Mahmoud Ahmadinejad’s announcement that he has ordered 20 percent uranium enrichment does not provide a good sign in this respect. There is some evidence that Tehran may not have the capacity to do this at the moment, if one is to go by some Western press reports. The point is not this, however.
The point is that Iran insists on playing a dangerously defiant game. And this is happening regardless of the extremely friendly exhortations from Turkey, which today acts more like an advocate of that country against the West than a neutral nation trying to broker an understanding between the two sides.
It is this attitude of Turkey’s that has complicated the country’s own position. Put simply, by cozying up to the increasingly despotic Ahmadinejad regime – and many argue this is due to feelings of Islamic solidarity – the Turkish government has undermined its chances for mediation with regard to this topic.........Foreign Minister Davutoğlu’s mission to Tehran will be critical and represent a litmus test for his own foreign-policy administration. After all, he is the principal author of the argument about Turkey’s rising influence in the Middle East.
So far, however, this influence has brought few results, whether these be between Israel and Syria, Hamas and the PLO or otherwise. So if he can not produce any results on Iran, this will not be a surprise for the majority of Western diplomats this writer knows in Ankara.
It is clear, however, that this outcome will also tarnish Turkey’s image as a rising regional power that can play a key role between the West and Islamic countries. The stakes, therefore, are higher for Ankara in this gambit than first meets the eye.