An estimate of the gluon contribution ΔG to the target-proton spin arising due to the anomaly in the singlet axial-vector current is made by using the axial-vector-current divergence equations. A particular combination of these divergences allows the above estimate without any detailed assumptions about proton matrix elements of pseudoscalar densities or of current quark masses. This estimate indicates that ΔG̃ [the SU(3)-singlet part of the gluon contribution ΔG] is negative but small. Further it is shown that the quark content of the proton spin is zero irrespective of the value of ΔG̃.

• Received 4 October 1989

DOI:https://doi.org/10.1103/PhysRevD.41.3517