**13. Limitations**

Study on the MT structure of plant and their function are impaired by difficulties that are encountered in the purification of this proteins since the innate bases, mostly because of intrinsic variability of the cysteine rich polypeptides with the occurrence of oxygen. Very few MTs are recuperated from the plant cells, and are uniform some as integral, noncleaved collections of metal [6]. The heterologous countenance approaches stunned this complications, but the early results exhibited as the pea MTs produced in *Escherichia coli* as innate protein were likewise vulnerable to proteolysis. Alternative strategies for producing the plant MTs as the fusion proteins generated some intact proteins that retained their metal binding and their antigenic features [43]. Inappropriately, the cleavage and the retrieval of MTs portion were not made and so the description of the consistent collections of metals were not shown. But, GST founded expression system are functional to various inborn MT forms allows amalgamation of huge quantity of the identical metal MT provisions. The investigation of this developments by the spectrometric and the spectroscopic systems have given some unparalleled data about the MT collective stoichiometric and the manageable performance of MTs [44].
