…or ATP-[gamma]-S? There was that little box which usually means some sort of non-displayable character in the font set. Anyway, ATP-gamma-S is an ATP analogue in which the gamma-phosphate atom is replaced by a sulfur atom, if that’s what you were wondering. The compound binds like ATP, but doesn’t react like ATP.
to clarify on the post about ATP[gamma]S. When the gamma-P is replaced with an S, then that bond can no longer be cleaved (i.e. ATP->ADP). Thus, people use the "non hydrolyzable" form of nucleotides to study enzyme activity when you don’t have to worry about substrate depletion