ENZYME ACTIVITIES ASSOCIATED WITH RIBOSOMES FROM SOYBEAN SEEDLINGS

Abstract

Ribosomes from cotyledons of soybean seeds soaked overnight in water (resting-cotyledon ribosomes) and respective ribosomes from cotyledons (working-cotyledon ribosomes) and hypocotyls (hypocotyl ribosomes) of 5 day-old seedlings were prepared. These ribosomes mainly consisted of 80 S particles. However, hypocotyls contained 115 S particles in a small amount and working-cotyledons contained 115 and 150 S particles which may correspond to the polymers of ribosomes or polysomes. The abundant 80 S ribosomes were fractionated by the sucrose density gradient centrifugation, and enzyme activities in the fractionated ribosomes were estimated. RNase, PDase, acid phosphatase, 5′-nucleotidase, XTPase, peroxidase and β-glucosidase were found in the ribosomes. The enzyme activities were lower in the resting-cotyledon ribosomes and higher in the hypocotyl ribosomes. Working-cotyledon ribosomes showed the middle of them. All these enzymes were also found in the cytoplasmic solution (supernatant) of cotyledon and hypocotyl cells. However, RNase, PDase, 5′-nucleotidase and peroxidase were concentrated in ribosomes, and the specific activities of 5′-nucleotidase and β-glucosidase were increased by washing the ribosomes. The status of the enzymes found in the ribosomes was discussed.