Making the Profit Center Field mandatory for Plant

Hi,

We have to make the Profit center field (MARC-PRCTR) mandatory for few Plants for Material Master Creation (MM01). We created a new Field reference under the Field selection group 48 and made it an Optional Entry. Still, in the material master creation the field remained mandatory.

Pls advise asap.

Thnx & Rgds,

Shekhar