Recently several natural anion-conducting channelrhodopsins (ACRs) were identified in several unicellular algae. Some of these light-gated ion channels have a high unitary conductance. My work focuses on the identification of residues and structural elements of the ACRs that have an influence on the conductance of ions. The gained knowledge could be used to increase the ion conductance of pourly conducting channelrhodopsins. Mutants of ACRs are constructed using the well-established QuikChange PCR mutagenesis. To obtain information about the unitary conductance noise analysis of electrophysiological recordings is utilized.