  Experimental Coulomb sum values of 6^Li and 7^Li nuclei have been obtained,
extending the earlier reported momentum transfer range of Coulomb sums for
these nuclei up to q = 0.750 ... 1.625 fm^-1. The dependence of the Coulomb
sums on the momentum transfers of 6^Li and 7^Li is shown to differ
substantially from similar dependences for all the other nuclei investigated.
Relationship between the nuclear cluster structure and Coulomb sums has been
considered. The momentum transfer value, above which the Coulomb sum becomes
constant, is found to be related to the cluster isolation parameter x, which
characterizes the degree of nuclear clusterization.
