A 10 kD barley seed protein homologous with an α-amylase inhibitor from Indian finger millet

Abstract

A basic protein was isolated from aqueous extracts of barley seeds. It contains 91 amino acid residues including 8 half-cystines, but no phenylalanine or tryptophan; the calculated molecular weight is 9,694. Amino acid composition and N-terminal sequence show that the protein corresponds to the probable amylase/protease inhibitor (PAPI) encoded by a formerly described cDNA. The protein is 50% homologous with an a-amylase inhibitor I-2 from seeds oflndian finger millet and it shows a distant homology with two Bowman Birk type protease inhibitors. However, the barley protein does not inhibit any of the enzymes tested. They include a-amylases, a 13-amylase. [3-glucanases. serine proteases, a sulfhydryl protease, aspartate proteases, and serine carboxypeptidases. Nevertheless. difference UV-spectroscopy indicated that the protein interacts with porcine pancreatic a-amylase. NMR-spectroscopy revealed that it possesses tertiary structure.

A 10 kD barley basic protein transfers phosphatidylcholine from liposomes to mitochondria

“…We therefore propose that it is classified as a barley lipid transfer protein (LTP) with the gene symbol Ltp replacing the former designations PAPI (6) and Ipa (11), respectively. The protein and its messenger are abundant in barley seeds (6,7). The mRNA is present not only during the latter half of seed development but also in the mature and germi;, nating seed in the aleurone (6, 7), which tissue is characterized by the presence of large numbers of oleosomes (2).…”

“…Protein was purified from barley flour essentially as described previously (7). After the separation on CM-cellulose and Sephadex G75, protein was lyophilized without desalting and stored at-18 ~ Its protein content of 37.3% was determined on the basis of amino acid analysis (7).…”

“…After the separation on CM-cellulose and Sephadex G75, protein was lyophilized without desalting and stored at-18 ~ Its protein content of 37.3% was determined on the basis of amino acid analysis (7). A sample of desalted 10 kD protein was prepared as described using Sephadex G25 and lyophilization.…”

“…Several years ago an abundant basic protein of circa 10 kD was isolated from barley seeds (caryopses) and the sequence of its 42 amino terminal residues plus the identity of its carboxyl residue determined (7). Simultaneously a full length clone from a barley aleurone cDNA library was characterized (6).…”

Identification of a 28,000 Dalton endochitinase in barley endosperm

“…Protein K with a molecular weight of 30,000 Dalton has been shown to be a protein synthesis inhibitor, PSI (2,6). The amino acid sequence ofa 10,000 Dalton protein (probably the basic protein N) has been deduced from a cDNA sequence (14) and in part, from amino acid sequencing (22). Its close homology with an a-amylase inhibitor isolated from ragi (5) was demonstrated, but no biological function as an inhibitor of amylases or proteases has yet been found.…”