data zinc;
  infile 'zinc.txt';
  input copper zinc protein;
     
proc glm;
  class copper zinc;
  model protein  =  copper zinc;
  estimate 'linear copper' copper -2 -1 0 1 2;
  estimate 'linear copper (alt)' copper  -75 -37.5 0 37.5 75;

  estimate 'linear zinc' zinc -2 -1 0 1 2;