Abstract
The principal pathways in the enzymic degradation of yeast ribonucleic acid by Aspergillus oryzae var. No. 13 have been established as shown in Figure 14, mainly by means of characterization of enzymic degradation products. Paper electrophoresis, paper chromatography, and ultraviolet spectrophotometry were employed for characterization.
Ribonucleodepolymerase degrades yeast ribonucleic acid into 3′ (or 2′)- adenylic, 3′ (or 2′)-guanylic, 3′ (or 2′)-cytidylic, and 3′ (or 2′)-uridylic acids without liberation of inorganic phosphate. It does not degrade sperm deoxyribonucleic acid. The activity is still preserved after dialysis and contact with weak-base anion exchange resin (Amberlite IR-4B) or Japanese acid clay. This enzyme is remarkably thermostable, especially in the range of pH from 5.5 to 6.5. In 0.05N sodium acetate solution 94% of the activity is retained after heating for 10 minutes at 100°C. The optimum conditions for the activity are at about 60°C and pH 4.0. This enzyme is not influenced by ninhydrin, monoiodoacetate, potassium cyanide, as well as sodium fluoride.
Mononucleotide phosphatase is thermolabile, and readily inactivated by physical or chemical treatments. Evidence suggests that this enzyme has properties similar to those of the general acidic phosphomonoesterase of plant origin. A brief procedure has been devised for the simultaneous detection of ribonucleodepolymerase and mononucleotide phosphatase on an agar plate.
The splitting of inosine and guanosine is carried out by nonphosphorolytic hydrolase. Adenosine, cytidine, and uridine are not split by the Aspergillus oryzae enzyme.
The direct liberation of hypoxanthine from 5′-inosinic acid by hydrolysis was first recognized. The enzyme responsible for this reaction is a nonphosphorolytic hydrolase and attacks 5′-inosinic acid specifically. Thus it seems that "5′-inosinate-N-ribosidase" might be an appropriate name for this enzyme.
