The Application relates to methods, and systems for nucleotide sequencing comprising producing polymerase reactions that comprise both catalytic and non-catalytic divalent metal ions. Polymerase/template/primer complexes are immobilized on a substrate. The complexes are exposed to a solution comprising a non-catalytic metal and nucleotides labeled with a detectable label on a portion of the nucleotide that is released upon incorporation. The cognate nucleotide is sequestered in the active site of the polymerase, unable to proceed to incorporation. After observing the sequestered cognate nucleotide, the complex is exposed to a catalytic metal, resulting in the incorporation of the bound cognate nucleotide and consequent release of the label resulting in a single-base extended primer.