iProcurement- Requisition submission only by buyer

Hi Gurus,

Is there a way to ensure only buyers (employees setup as buyers) can submit requisition?

The standard PO creation will require you to be a buyer in order to access the PO entry form- is there some thing similar we can achieve for iProcurement?

We have the system setup in a way - once the requisition is submitted and all approvals are secured, the workflow will automatically create Approved PO. But for automatic creation of PO,system requires the preparer to be a buyer. In a case where a non buyer submits the requisition, the PO is not created and we have to manually autocreate. So for this reason we want a control on requisition entry itself to check if the preparer is a buyer too.