Direct photon cross sections obtained in pp and pp collisions at √s = 24.3 GeV at the CERN SPS, are used in a next-to-leading order QCD analysis. From the cross-section difference σ(pp → γX) - σ (pp → γX), and quark distributions measured in deep inelastic scattering, a determination of the strong coupling constant, αs, is performed via a measurement of Λ (4) MS. This first measurement of Λ (4) MS using direct photon data yields a value Λ (4) MS = 235 ± 79 (stat.) ± 70 (syst.) MeV. The corresponding value of αs expressed at MZ2 is αs (MZ2) = 0.112±0.006 (stat.)±0.005 (syst.)-0.001+0.009 (theor.). The gluon distribution in the proton for x > 0.2 is determined both from the pp and from the pp data, and the results agree with each other and with previous determinations using the same method.