Behavior of O-glycosyl and O-phosphoryl proteins in alkaline solution.
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Post-translational modifications (PTMs) regulate protein function across all life forms and allow plants to respond rapidly to biotic and abiotic stress. Over 450 PTM types have been described across organisms, of which 23-33 have been experimentally confirmed in plants, including phosphorylation, acetylation, methylation, glycosylation, ubiquitination, and sumoylation. These modifications are highly dynamic and often reversible, and frequently act in combination, or "crosstalk," to fine-tune cellular processes. Advances in high-resolution mass spectrometry and large-scale genome sequencing continue to expand the catalogue of known PTM sites, while machine learning and deep learning approaches increasingly support prediction of PTM site localization and function. Unlike broader surveys of plant PTMs, this review focuses specifically on O-phosphorylation and Lys-N(ε)-acetylation, the two best-characterized and most extensively crosstalking PTMs in plants, and integrates four perspectives: the historical development of proteomic and bioinformatics approaches to these modifications; current mass spectrometry-based workflows and enrichment strategies; the bioinformatics tools and databases available for their analysis; and the technical and species-related challenges, particularly in non-model plants, that currently limit their study. We close by outlining priority directions for future research, including multi-omics integration, AI-based prediction, and the translation of PTM knowledge into crop stress resilience and breeding applications.
Human liver contains three chromatographically distinct forms of non-specific acid phosphatase (EC 3.1.3.2). Acid phosphatases I, II and III have molecular weights of greater than 200 000, of 107 000, and of 13 400, respectively. Following partial purification, isoenzyme II was obtained as a single activity band, as assessed by activity staining with p-nitrophenyl phosphate and alpha-naphthyl phosphate on polyacrylamide gels run at several pH values. With 50mM p-nitrophenyl phosphate as a substrate, enzymes II and III exhibit plateaus of activity over the pH range 3 - 5 and 3.5 - 6, respectively. Acid phosphatase II is not significantly inhibited by 0.5% formaldehyde. The activity of human liver acid phosphatase II and of human prostatic acid phosphatase towards several substrates is compared. The liver enzyme, is marked contrast to the prostatic enzyme, does not hydrolyze O-phosphoryl choline.