The correct option is A K
Enzymes requires metal ion as a cofactor which activates their catalytic activity. For example carbonic anhydrase and alcohol dehydrogenase require zinc, arginase and ribonucleotide reductase require manganese, dinitrogenase and nitrate reductase require molybdenum, pyruvate kinase requires potassium. The metal ions Mo, Zn and Mn are present at the active site of enzymes and the respective enzymes are called metalloproteins but potassium requiring enzymes are not metalloproteins as it is not a part of enzyme but it activates the enzyme.