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The three globulins of the seeds of L. angustifolius cv. Uniwhite may be satisfactorily resolved in 10 min by electrophoresis on cellulose acetate strips. These globulins, conglutins α, β and γ, vary markedly in their amino acid compositions, with conglutin Ω differing from conglutins α and β and most other legume storage proteins in its relatively high content of cystine and methionine and lower content of arginine and glutamic acid. When examined on sodium dodecyl sulphate-polyacrylamide gels, both in the absence and presence of β-mercaptoethanol, the three globulins were found to differ completely in the type of subunit proteins they contain and in the significance of intrachain disulphide bonding. Conglutin α was found to contain three or four types of non-covalently linked subunits with apparent molecular weights in the range 55 000-80 000, each of which may contain a disulphide-bonded moiety with a molecular weight near 20 000. Conglutin γ was found to contain disulphide-bonded chains of molecular weights 17 000 and 30 000, whereas the four major subunits of conglutin β, whose molecular weights lie in the range 20 000-60 000, were not covalently linked together. The latter globulin does not appear to be homogeneous, for it can be separated by fractional precipitation with ammonium sulphate into a series of fractions which differ markedly in the proportion of subunit types they contain.

Pea albumin 2 (PA2:Mr≈26000) is a major component of the albumin fraction derived from aqueous salt extracts of pea seed. Sodium dodecylsulfate-polyacrylamide gel electrophoresis and chromatography on DEAE-Sephacel resolve PA2 into two closely related components (PA2a and PA2b). A cDNA clone coding for one of these components has been sequenced and the deduced amino acid sequence compared with partial, chemically-determined sequences for cyanogen bromide peptides from both PA2 components. Complete amino acid sequences were obtained for the C-terminal peptides. The PA2 molecule of 230 amino acids contains four imperfect repeat sequences each of approximately 57 amino acids in length.The combined sequence data, together with a comparison of PA2-related polypeptides produced in vitro and in vivo, indicate that PA2 is synthesized without a signal sequence and does not undergo significant post-translational modification. Although both forms of PA2 contain Asn-X-Thr consensus sequences, neither form is glycosylated. Accumulation of PA2 contributes approximately 11% of the sulfur-amino acids in pea seeds (cysteine plus methionine equals 2.6 residues percent). Suppression of levels of PA2 polypeptides and their mRNAs in developing seeds of sulfur-deficient plants is less marked than that for legumin, in spite of the lower content of sulfur-amino acids in legumin.

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Seeds from L. angustifolius grown at three levels of applied sulphur contain similar amounts of protein whereas the ratio of total nitrogen to total sulphur in the whole seed and in the extracted protein is greatly increased under sulphur deficiency. This large change in nitrogen to sulphur ratio is accompanied by suppression of the synthesis of conglutins α and γ which usually contain most of the sulphur-containing amino acids found in these seeds. This is balanced by synthesis of an increased amount of conglutin β which normally contains no methionine and a lower proportion of cystine. Studies of the protein subunit composition show that the overall molecular weight distribution of the polypeptides is independent of the level of sulphur, but under sulphur deficiency the higher molecular weight subunits do not contain the disulphide linkages normally present. It is not known whether these higher-molecular-weight conglutin β subunits are normally absent or present only in trace amounts in the seeds.

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Recent studies in a number of laboratories have characterised many of the properties of a major pea albumin (designated PMA or PA2: subunit M,-26000) which is not readily degraded in the cotyledon upon germination. In the present report, some of the physicochemical properties of this protein have been studied in greater detail. A non-helical structure, stable at high pH, is evident. Of special significance is the presence of a single free sulphydryl group, although studies reported elsewhere show that the protein consists of four copies of a strongly conserved repeated sequence. It is postulated that this free sulphydryl group in PA2 (5-10% of total pea seed protein) causes polymerisation through disulphide interchange and thereby is a likely source of partial insolubility in protein isolates following an initial alkaline extraction.