Proton cotransport of thiourea in Chlorella fusca

Abstract Active thiourea uptake by Chlorella fusca var. vacuolata was accompanied by a simultaneous uptake of protons. The ratio of uptake of protons: uptake of thiourea was 0.92 (average of 5 experiments). The half maximal rate of proton uptake occurred at a thiourea concentration of 62 μM. Rate of thiourea uptake was highest at pH 5.5 and fell to 20% of the maximal rate as pH was increased to 8.0. It is concluded that thiourea is transported into Chlorella by a proton cotransport system similar to that known for glucose transport.