Enzymatic degradation of standard kappa-carrageenan and the low-gelling hybrid kappa-/mu-carrageenan were conducted using recombinant Pseudoalteromonas carrageenovora kappa-carrageenase. The initial velocity of the enzyme was determined as, a function of varying Tris or Nal concentrations and at constant 200 mM cosolutes concentration, adjusting Nal and Tris concentrations accordingly. In both cases, we observed strong inhibition of the enzyme with increasing amounts of iodide. The characterization of the kappa- and kappa-/mu-carrageenan ordering by optical rotation and the visualization of iodide binding on carrageenan by I-127 NMR revealed that inhibition was not caused by the disordered-ordered transition of carrageenan in Nal, but by iodide binding. These results were confirmed by analysis of the degradation products by gel permeation chromatography. Degradation of carrageenan in the disordered state led to a rapid decrease in molecular mass and the production of all possible neo-kappa-carrabiose oligomers. In the ordered conformation, the degradation kinetics, the decrease of average molecular weight, and the chain population distribution of degradation products varied with iodide concentration. These observations were interpreted to be the result of increasing amounts of bound iodide on carrageenan helices that, in turn, impede enzyme catalysis. Based on these results, we propose a single-helix ordered conformation state for kappa-carrageenan and reject the previously advocated double-helix model.