  Five-dimensional field theories compactified on an S^1/Z_2 orbifold naturally
include local brane kinetic terms at the orbifold fixed points at the tree as
well as the quantum level. We study the quantization of these theories before
the Kaluza--Klein reduction and derive the relevant Ward and Slavnov-Taylor
identities that result from the underlying gauge and Becchi-Rouet-Stora
symmetries of the theory. With the help of these identities, we obtain a
generalization of the equivalence theorem, where the known high-energy
equivalence relation between the longitudinal Kaluza-Klein gauge modes and
their respective would-be Goldstone bosons is extended to consistently include
the energetically suppressed terms in the high-energy scatterings. Demanding
perturbative unitarity, we compute upper limits on the number of the
Kaluza-Klein modes. We find that these limits weakly depend on the size of the
brane kinetic terms.
