The influence of nickelous ions on carbohydrate transport in yeast cells

Abstract

• 1.

  1. It has been postulated that active trans-membrane transport of metabolizable sugars has at least four steps. The overall transport is inhibited by nickelous ions and the inhibition appears to be caused by an interaction of nickelous ions with polyphosphates, which are postulated to be involved in one of the steps of the transport mechanism.

• 2.

  2. The characteristics of the transport of sorbose in normal, and of glucose in iodoacetate-poisoned cells are different from this active transport mechanism and can be described as carrier-mediated facilitated diffusion. Polyphosphates are not involved in facilitated diffusion nor is this inhibited by nickelous ions.

• 3.

  3. Ni²⁺ inhibition of active transport increases strongly with increasing temperature. This is caused by a considerable decrease of the energy of activation of the transport process by nickelous ions. Different steps of the individual transport processes appear to be rate-limiting in normal and in Ni²⁺-inhibited sugar influx.

• 4.

  4. The affinity of sugars for the transport system is not influenced by nickelous ions.

• 5.

  5. Experimental results with combinations of two metabolizable sugars in the medium indicate the existence of at least two sugar carriers in the yeast cell membrane: one for the hexoses and one for maltose.