Light strongly interacting supersymmetric particles may be treated as partonic constituents of nucleons in high energy scattering processes. We construct parton distribution functions for protons in which a light gluino is included along with standard model quark, antiquark, and gluon constituents. A global analysis is performed of a large set of data from deep-inelastic lepton scattering, massive lepton pair and vector boson production, and hadron jet production at large values of transverse momentum. Constraints are obtained on the allowed range of gluino mass as a function of the value of the strong coupling strength ${\ensuremath{\alpha}}_{s}({M}_{Z})$ determined at the scale of the $Z$ boson mass. We find that gluino masses as small as 10 GeV are admissible provided that ${\ensuremath{\alpha}}_{s}({M}_{Z})\ensuremath{\ge}0.12$. Current hadron scattering data are insensitive to the presence of gluinos heavier than $\ensuremath{\sim}100--150\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$.