Does the non-saturable cell entry apply to the charge-free form of amino acids?

The slow cellular entry shown by neutral alpha-amino acids at very high concentrations appears not to arise from diffusion of the totally uncharged species through the plasma membrane of the Ehrlich cell, judging from a similarity of the rates observed for the two conformational isomers of 1-amino-2-hydroxy-cyclohexane-carboxylic acid. One of these isomers provides in neutral solution 4 times as large a proportion of the charge-free species as the other, and 5 times the proportion calculated for alanine.