Answer: For (a):
(Lys-Ala)3 is soluble and (Gly)zo is not soluble.
(b) (Glu)zo is soluble and (Phe-Met) is not soluble.
(c) ( Asn-Ser-His) is soluble and (Ala- Asp-Gly) is not soluble.
(d) (Asn-Ser-His) is soluble and (Ala-Ser-Gly).
Explanation:Firstly, the solubility of polypeptides relies on polar groups in the R group of the side chain and also ionized groups because these groups can interact with dipole bond of water.
For (a): (Gly)zo, no R group of the side chain of (Gly)zo is polar nor ionizable and solubility is based on the ability of R group of polypeptides to be polar or ionized while in polypeptides of (Lys-Ala), Lys is polar and therefore soluble though Ala in the compound is not polar nor ionizable but the presence of Lys makes the polypeptide to be soluble.
(b) (Glu)zo is a polar peptide, therefore soluble peptides while both the combination of (Phe-Met)3 gives polypeptides that are not polar therefore not soluble.
(c) In poypeptide of (Ala-Asp-Gly)s, the R group on the side chain of both Ala and Gly are neither polar nor ionizable therefore cannot be soluble even though Asp( which at PH 3 can partially be protonated and partially deprotonated to make it soluble) is present in the polypeptide. Therefore the polypeptide of Ala-Asp-Gly is not soluble compared to Asn- Ser-His, where Asn has polar covalent bond which can interact with water, His which at pH 6 will be half protonated and half deprotonated making the substance to react with water and also Ser is a soluble polypeptide too.
(d) Also between (Ala- Ser-Gly) and ( Asn- Ser-His), polypeptide with (Asn-Ser-His) will be considered soluble because Ala and Gly have R groups that neither polar nor ionizable though Ser is soluble but common to both substances, its influence will not be effective and (His) is a soluble which at pH 6 get partially protonated and deprotonated.
