We have measured the low-temperature electron transport properties in a fro
nt-gated GaAs/Al0.33Ga0.67As heterostructure. Collapse of spin-splitting an
d an enhanced Lande \g\-factor at both Landau level filling factors nu = 3
and nu = 1 were observed. Our experimental results show direct evidence tha
t the electron-electron interactions are stronger at v = 3 than those at v
= 1 over approximately the same perpendicular magnetic field range. Moreove
r, we observed an enhancement of the magnetoresistivity of a two-dimensiona
l electron system with an increasing parallel magnetic field. Using a simpl
e model, we suggest that the increase of the magnetoresistivity is due to s
pin but the model over-estimates the Lande \g\ factor in our system.