Portal de Periódicos da CAPES

Properties, biosynthesis and processing of a sulfur‐rich protein in Brazil nut ( Bertholletia excelsa H.B.K.)

1987; Wiley; Volume: 162; Issue: 3 Linguagem: Inglês

10.1111/j.1432-1033.1987.tb10665.x

1432-1033

Samuel S. M. Sun, Susan B. Altenbach, Filomena W. Leung,

Insect and Pesticide Research

An abundant seed protein, which is exceptionally rich in the sulfur-containing amino acids, methionine (18%) and cysteine (8%), is synthesized in Brazil nut embryos about 9 months after flowering. This sulfur-rich protein consists of two low-molecular-mass polypeptide components, a 9-kDa polypeptide and a 3-kDa polypeptide. The two-subunit polypeptides associate through disulfide linkage(s) to form a 12-kDa protein molecule. We have demonstrated through in vitro translation studies, using RNA from 9-month-old embryos, that the sulfur-rich protein is synthesized as a larger precursor polypeptide of 18 kDa. In addition, data from in vivo labelling studies of 9-month-old Brazil nuts suggest that there are two intermediate precursors of the sulfur-rich protein, one of 15 kDa and another of 12 kDa. One of these precursors, the 12-kDa polypeptide, accumulates for a 2-month period in the developing embryos. From these data we infer that at least three stepwise cleavages are involved in the maturation of the sulfur-rich protein from its 18-kDa precursor.