  We consider some implications of the mass defect on the frequency of atomic
transitions. We have found that some well-known frequency shifts (gravitational
shift and motion-induced shifts such as: quadratic Doppler and micromotion
shifts) can be interpreted as consequences of the mass defect in quantum atomic
physics, i.e., without the need for the concept of time dilation used in
special and general relativity theories. Moreover, we show that the inclusion
of the mass defect leads to previously unknown shifts for clocks based on
trapped ions.
