4-aminobutanoate + L-histidine + ATP => L-homocarnosine + ADP + phosphate + H(+)
4-aminobutanoate + l-histidine + atp => l-homocarnosine + adp + phosphate + h(+)
4-aminobutanoate + L-histidine + ATP => L-homocarnosine + ADP + phosphate + H(+)
4-aminobutanoate + l-histidine + atp => l-homocarnosine + adp + phosphate + h(+)