Pyruvate carboxylase activation:

Oxaloacetate has two major roles. It is an intermediate which is consumed in gluconeogenesis and it is also a key intermediate in the citric acid cycle where it fuses with acetyl CoA to form citrate, finally being regenerated through the cycle. Therefore pyruvate carboxylase produces oxaloacetate for gluconeogenesis but also must maintain oxaloacetate stages for citric acid cycle function.  Intended for the latter reason the  activity  of  pyruvate  carboxylase   depends  absolutely  on  the  presence  of acetyl  CoA; the biotin  prosthetic  set  of the enzyme  cannot  be carboxylated unless  acetyl  CoA is bound  to the enzyme.  This allosteric activation through acetyl CoA ensures which more oxaloacetate is made when excess acetyl CoA is available. In this role of maintaining the level of citric acid cycle intermediates and the pyruvate carboxylase reaction is said to be anaplerotic which is filling up.