  We propose a new analytic scaling of the cut-off frequency of synchrotron
radiation from active galactic nucleus (AGN) jets that are nonuniformly filled
with many filaments. The theoretical upper limit is provided independent of
magnetic intensity, spectral index, coherence and correlation length of
filamentary turbulence, etc., such that \nu_c\simeq 6\times
10^{20}\delta[(r-1)/r]^{4/3}(b/10^{-4}) Hz, where \delta, r and b are the
Doppler beaming factor, shock-compression ratio and energy-density ratio of the
perturbed/local mean magnetic field of the filaments, respectively. Combining
our results with observational data for 18 extragalactic sources, a constraint
on the filament correlation length is found, in order to give the number
scaling of filaments. The results suggest that, in particular, the jets of
compact BL Lacs possess a large number of filaments with transverse size scale
smaller than the emission-region size. The novel concept of the quantization of
flowing plasma is suggested.
