Portal de Periódicos da CAPES

The ratio of free to membrane-bound chloroplast ribosomes

1973; Elsevier BV; Volume: 324; Issue: 4 Linguagem: Inglês

10.1016/0005-2787(73)90211-6

1879-3002

K. Tao, André T. Jagendorf,

Mass Spectrometry Techniques and Applications

In isolated chloroplasts of pea and spinach, some ribosomes remain associated with green thylakoid membrane during repeated washings in hypotonic media. Attempts were made to estimate the proportion of the total chloroplast ribosomes apparently bound to membranes. Chloroplasts were prepared in which the majority retained stroma material as indicated by Class I morphology in phase-contrast microscopy, and by the failure to photoreduce ferricyanide anions until subjected to hypotonic disruption. Nevertheless judging by the distribution of the ribulose diphosphate carboxylase (Fraction I) protein in the homogenate, major amounts of stroma material have been lost depending on the care used in isolation. The ratio of free to bound ribosomes in these chloroplasts ranged between 1 and 2.5 to 1. Pea leaf chloroplasts were also isolated by non-aqueous prodecures. These contained the same amount of bound ribosomes as those prepared in aqueous media, but up to 4 times as many free 70-S chloroplast ribosomes. Electrophoresis of the rRNA from these preparations from pea leaves showed no contamination by 80-S ribosomes, and both rRNA species appeared to be stable during further extraction procedures. With non-aqueous isolated chloroplasts, the ratio of free to bound ribosomes was 4.5 to 1 for peas. These values agreed with those calculated from results with aqueous chloroplasts, based on the proportion of total ribulosediphosphate carboxylase lost.