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Patterns of Urease Synthesis in Developing Soybeans ¹

Biochemistry Department, University of Missouri, Columbia, Missouri 65212, Scripps Clinic and Research Foundation, La Jolla, California 92037

An examination of in vivo polysome-bound activity indicates that soybean (Glycine max, cv. Prize) seed urease is synthesized on large polysomes (n 15). In vitro urease synthesis is directed by a large RNA (3,000-3,300 nucleotides). Urease synthesis occurs throughout the normal protein biosynthetic phase of the developing seed. Surprisingly, the activity/antigen ratios of urease increase throughout development. Urease appears to be in a more highly polymerized state in mature beans versus beans in early development.

During the 55 days from pollination to maturity, urease specific antigen (antigen versus total seed protein) is greatest on the 20th day, representing 0.6% of total extractable protein. Its synthesis proceeds until the end of the protein biosynthetic phase, approximately day 40. In contrast, the appearance of urease enzyme activity lags that of antigen during early development (11-20 days) and plateaus in late development. Mixing experiments suggest no role for putative urease inhibitors or activators during development. However, several electrophoretically slow migrating forms are unique to the urease of mature beans. It is not known if these are more active species.

An active urease species exhibits an RNAse-sensitive cosedimentation with a heavy polyribosome class (n 15). Polyadenylated RNA, size-fractionated to 3,000 to 3,300 bases, directed the synthesis in vitro of a major translational product electrophoretically and immunologically similar to the in vivo-synthesized urease subunit.

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