cytosine(out) + H(+)(out) => cytosine(in) + H(+)(in)
cytosine(out) + h(+)(out) => cytosine(in) + h(+)(in)
cytosine(out) + H(+)(out) => cytosine(in) + H(+)(in)
cytosine(out) + h(+)(out) => cytosine(in) + h(+)(in)