Eukaryotic Polypeptide Elongation System and Its Sensitivity to the Inhibitory Substances of Plant Origin

Abstract

Abstract

The structural and functional characteristics of the elongation system (ri-bosomes and elongation factors) are presented. The immunochemical and diagnostic meaning of the ribosome investigations is considered. Evidence of the participation of ribosomes in the first step of protein glycosylation is presented.

The heterogeneous elongation factor eEF-1, isolated from Guerin epithelioma, can be separated into three fractions: one of them functionally corresponds to EF-1α, the second one to EF-1βγ, and the third is an unidentified, active aggregate named EF-1B, which contains the subunit forms EF-1α and EF-1βγ, and other polypeptides showing protein kinase activity. The aggregate EF-1B can be autophosphorylated, while the subunit forms EF-1α and EF-1βγ can neither become autophosphorylated nor phosphorylate other polypeptides. The subunit form EF-1βγ consists from two polypeptides of 32 and 51 kDa, corresponding to other eukaryotic β and γ polypeptides, respectively. EF-1βγ is thermostable and protects against thermal inactivation of EF-1α in the EF-1α-EF-1βγ complex.

Pure eEF-2 preparations isolated from normal and neoplastic tissues show different structural features. The existence of eEF-2 in multiple forms, differing in molecular mass, have been found. The eEF-2 with molecular weight of about 100 kDa can be phosphorylated, while eEF-2 of about 65 kDa was not phosphorylated by protein kinase eEF-2. The phosphorylated eEF-2 lost its activity, and this effect was reversed by dephosphorylation. The eEF-2 (65 kDa) was isolated from the active polyribosomes, and it may directly participate in the translocation step of the peptide elongation.

It was noted that the components of elongation system can be inhibited, in separate steps, by the substances isolated from various sources of plant origin. Alkaloids emetine and cepheline, cardiac remedy digoxin, saponin glycoside, and its aglycon directly inactivated ribosomes. Quercetin inhibited eEF-1 activity by directly influencing its subunit form EF-1α. eEF-2 was shown to be a target site of the inhibitory action of the glycoside isolated from Melissa officinalis leaves. [P.S.E.B.M. 1996, Vol 212]