| Budget Amount *help |
¥7,200,000 (Direct Cost: ¥7,200,000)
Fiscal Year 1986: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1985: ¥6,200,000 (Direct Cost: ¥6,200,000)
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| Research Abstract |
Many plants contain two types of PSI, Type <I> and Type <II> . We have isolated Type <I> PSIs from seeds of Luffa cylindrica roem (luffin) and Phytolacca amiericana (PAP-S) and Type <II> PSI from seeds of Abrus precatorius (abrin A-chain), and investigated their amino acid sequences and amino acid residues involved in their activities. In this study, the sequencing of abrin A-chain was almost completely done, and about 75% abd 35% of the sequences of luffin and PAP-S were determined. In comparison with the sequences of four PSIs, it was found that Type <I> PSIs are Lys-rich proteins and highly homologous, whereas Type <II> PSIs are Arg-rich proteins bearing high homology to each other. Type <I> and Type <II> are homologous, but their amino acid sequences are markedly different.
By chemical modification, it was revealed that Arg residues are involved in the activity of all PSIs examined, but Trp residue and amino group also appear to be involved in the activity of abrin and luffin, respectively. Active Arg residue in ricin A-chain was found to be located in N-terminal region. Six common amino acid residues including the active Arg residue exist in their N-terminal regions, whereas there is no common residues in their C-terminal regions. Ricin A-chain which has been stripped 27 residues from its C-terminus has no activity in spite of its same chain-length as one of Type <I> PSI (trichosanthin). From these results, it was inferred that N-terminal region of PSI may participate their catalytic actions, while C-terminal region may be involved in their activity specificities.
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