Del'vig A A, Debov S S
Biokhimiia. 1976 Feb;41(2):335-42.
In vihro decay of rat liver polyribosomes is studied under conditions of occuring phosphorolytic activity of polynucleotidephosphorylase (PNPase) and, in contrast, excluding PNPase activity (in the absence of orthophosphate). The rate of polyribosome degradation is found to be higher in the presence of orthophosphate, than in its absence. Sedimentation coefficient of ribosomes formed from degraded polyribosomes in the absence of orthophosphate is 70S, while that of ribosomes formed under phosphorolysis is 67S. It is suggested that polyribosome degradation in the presence of orthophosphate is carried out by the combined action of 5'-RNase and PNPase. 5'-RNase degrades mRNA and rRNA without disturbing the integrity of ribosomal complexes, while PNPase phosphorolyzes the fragments formed from the 3'-OH terminal, successively releasing ribosomes. The rate of polysome inactivation in the presence of orthophosphate (half-life period being approximately 17 min) is considerably higher than that in the absence of orthophosphate (half-life period being 37 min). The amount of active polysomes in samples incubated for 3 hours both in the presence and in the absence of orthophosphate is 16% and 24% of the total amount of active polysomes, respectively. It is suggested that there are a certain type of polyribosomes, which comprise about 8% of polyribosomes that can be inactivated only by PNPase.
在体外，研究了大鼠肝脏多核糖体在多核苷酸磷酸化酶（PNPase）具有磷酸解活性的条件下以及相反地排除PNPase活性（在没有正磷酸盐的情况下）的衰变情况。发现存在正磷酸盐时多核糖体的降解速率高于不存在正磷酸盐时。在没有正磷酸盐的情况下由降解的多核糖体形成的核糖体沉降系数为70S，而在磷酸解作用下形成的核糖体沉降系数为67S。有人提出，在正磷酸盐存在下多核糖体的降解是由5'-核糖核酸酶和PNPase的联合作用进行的。5'-核糖核酸酶降解mRNA和rRNA而不破坏核糖体复合物的完整性，而PNPase磷酸解从3'-OH末端形成的片段，依次释放核糖体。在正磷酸盐存在下多核糖体失活的速率（半衰期约为17分钟）明显高于不存在正磷酸盐时（半衰期为37分钟）。在有和没有正磷酸盐的情况下孵育3小时的样品中活性多核糖体的量分别为活性多核糖体总量的16%和24%。有人提出存在某种类型的多核糖体，其约占多核糖体的8%，只能被PNPase失活。
