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Changes were studied in the bulk protein of tobacco leaves, lucerne shoots and sunflower-seed kernels subjected to aerobic autolysis at room temperature. Bulk-protein fractions from cigar and from commercial sunflower-seed meal were also examined. Quinic acid, released by cold alkaline hydrolysis, was used as a measure of binding of chlorogenic acid residues to the proteins. On aerobic autolysis, the proteins of the leafy materials underwent some proteolysis; chlorogenic acid residues became bound to the protein, with concomitant diminution of free chlorogenic acid. The proteins showed browning, increased ultraviolet absorption and diminished content and "chemical availability" of lysine. However, during aerobic autolysis, the bulk protein of sunflower-seed kernels did not couple appreciably with the chlorogenic acid congeners present; the above accompanying phenomena were also largely absent. It is concluded that, when protein-rich plant materials are to be fed to monogastric animals, and particularly when their lysine content is critical, more attention should be paid to effects of the polyphenols and polyphenol oxidases present in the original plant, IntroductionThe nutritive quality of proteins (and particularly the availability of their lysine residues) may be adversely affected by reaction of the protein with quinonoid oxidation products arising from plant polyphenols (for reviews see refs. 1 4 ) . However, relevant detailed studies are still scanty. Recently Mbadiwe,s working with seeds of the legume Pentaclethra macrophylla Benth., which are rich in N-caffeoylputrescine,6*7 observed that, during prolonged storage of the seeds in air at room temperature, their protein became brown, showed diminished "chemically available" lysine and yielded putrescine on acid hydrolysis. Pierpoint and colleagues*-ll observed, in the presence of polyphenol oxidases, coupling of chlorogenic acid (3-0-caffeoylquinic acid) with thiol groups of cysteine residues and with eNH2 groups of certain lysine residues in some well-characterised proteins. They demonstrated charge-reversal, with expected changes of electrophoretic mobility. Since tobacco is rich in chlorogenic acid (and its i~o m e r s ) , l~-~~ and is also the only plant other than Peiitaclethra so far shown to contain N-caffeoylputre~cine,~~-~~ we hoped to observe oxidative coupling of both of these compounds to the leaf proteins, with different effects on their electrophoretic mobilities. To work with tobacco leaf should have the additional advantage that its proteins have been subjected to closer physicochemical characterisation than those of most other leaves. However, preliminary studies by Dr E. I. Mbadiwe have confirmed the observations of others,l7-19 that N-caffeoylputrescine is confined to young shoots and flowers in the normal tobacco plant. Accordingly, the work now described was limited to study of the coupling of the bulk protein of fairly mature leaves with chlorogenic acid.In view of current commercial interest in "green-crop fractionation"20 and in the p...