Association of glyceraldehyde‐3‐phosphate dehydrogenase with mono‐and polyribosomes of rabbit reticulocytes

It has been shown recently that glyceraldehyde‐3‐phosphate dehydrogenase (GAPD) is one of the three major RNA‐binding proteins of rabbit reticulocytes [Ryazanov, A. G. (1985) FEBS Lett. 192, 131–134]. It was suggested that, due to its RNA‐binding capacity, GAPD can form loose dynamic complexes with polyribosomes. This communication reports that a considerable amount of GAPD activity can be found in the mono‐ and polyribosome fraction after sucrose gradient centrifugation of rabbit reticulocyte lysate. An increase of ionic strength, as well as the addition of exogenous RNA to the extract, result in the removal of GAPD from the complex with mono‐ and polyribosomes. It appears that GAPD forms the complex with polyribosomes due to the interaction with some exposed RNA regions of these structures. Although the interaction of GAPD with ribosomes is weak, it can be detected under physiological ionic conditions by the difference boundary sedimentation velocity technique. Association of GAPD with mono‐ and polyribosomes can be prevented by a low concentration (10 μM) of NADH, but not NAD⁺. A nitrocellulose filter binding assay also shows that NADH has a stronger inhibitory effect on the enzyme‐RNA complex formation, as compared with NAD⁺. We propose that the RNA‐mediated association of GAPD with mono‐and polyribosomes can provide compartmentation of the energy‐supplying system on these structures within the cell. This can maintain a high local concentration of ATP and GTP near the sites of protein synthesis.