The Effects of Hemin and Double-Stranded RNA on α and β Globin Synthesis in Reticulocyte and Krebs II Ascites Cell-Free Systems and the Relationship of These Effects to an Initiation Factor Preparation

Protein synthesis in reticulocyte lysates ceases abruptly in the absence of added hemin or in the presence of double-stranded RNA. A similar effect of double-stranded RNA is observed in Krebs II ascites cell-free systems translating exogenous globin mRNA. The shut-off of protein synthesis is due to inhibition of initiation and can be prevented or reversed by addition of the initiation factor preparation M(3). Preparations of M(1), M(2), and dissociation factor are ineffective under these conditions. The effects of added hemin, M(3), and globin mRNA on the synthesis of α and β globin chains have been studied in the reticulocyte and ascites cell extracts. When the concentration of M(3) is rate limiting, the synthesis of β chains exceeds that of α chains. When the concentration of mRNA is rate limiting, synthesis of α and β chains is more nearly equal

Contribution of an Ultrasonic Interferometry Method (Echocell) to the Determination of Red Blood Cell Sedimentation Rate at Low Hematocrit

The sedimentation rate ($SR$) of red blood cells (RBCs) in suspension was determined at low volume fractions (1%-5%) by a new ultrasonic interferometry method (EchoCell). This method is based on A-mode echography and measures the accumulation rate of RBCs on a solid plate during RBC settling. The RBC accumulation rate, which is related to the $SR$, is obtained from interference of waves reflected by the two interfaces “plate / sedimented particles” and “sedimented particles / suspension”. The method allows to distinguish $SR$ of RBCs with high and mean settling velocity. Present results are compared (i) to the experimental $SR$ measured by using a cylindrical tube of same geometry as the EchoCell cavity and (ii) to the theoretical $SR$ predicted by some models, especially the Kermack et al. one: the linearly relationship found between the volume fraction of RBCs (or hematocrit) and $SR$, obtained at low hematocrit using the ultrasonic interferometry method, agrees with the cylindrical tube method.La vitesse de sédimentation (VS) des globules rouges (GR) du sang, individuels, en suspension, a été déterminée par une méthode originale d'interférométrie ultrasonore (EchoCell). La méthode, dont le principe repose sur l'échographie mode-A, permet de mesurer la vitesse d'accumulation des GR sur un plan solide lors de leur sédimentation. La vitesse d'accumulation, qui est reliée à leur vitesse de sédimentation, est obtenue à partir de l'interférence des ondes réfléchies par les deux interfaces “plan solide / particules sédimentées” et “particules sédimentées / suspension”. La méthode permet de distinguer les vitesses de sédimentation de globules rouges à VS moyenne et élevée. Les résultats présentés sont comparables (i) aux mesures expérimentales utilisant un tube cylindrique de même géométrie que l'EchoCell et (ii) aux valeurs théoriques proposées par certains modèles et en particulier celui de Kermack et al.. La relation linéaire retrouvée entre la VS et l'hématocrite avec la méthode ultrasonore est concordante avec celle retrouvée en utilisant la méthode du tube cylindrique