Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.10.3.1 (tyrosinase)
 9,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Trematode parasites protect their eggs with a tough tanned eggshell. Eggshell precursor proteins are synthesized and stockpiled within the extensive vitellaria of the animal. A major eggshell precursor protein with an apparent molecular weight of 31,000 and pI of 7.4 was isolated from the vitellaria of Fasciola hepatica. This protein, which represents 6-7% of the total protein in mature Fasciola, is unique in containing rather high levels of the amino acid 3,4-dihydroxyphenylalanine (DOPA), i.e., 110 residues per 1000. Other prominent amino acids are glycine, aspartic acid, and lysine. A prominent DOPA-containing tryptic peptide derived from eggshell precursor protein has the sequence Gly-Gly-Gly-DOPA-Gly-Gly-DOPA-Gly-Lys. DOPA residues disappear during the maturation of the eggshell and by treatment in vitro with mushroom polyphenol oxidase. This disappearance may be related to the formation of cross-links in the eggshell protein.
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PMID:Presclerotized eggshell protein from the liver fluke Fasciola hepatica. 342 7

A tomato (Lycopersicon esculentum L.) gene encoding a precursor of polyphenol oxidase (PPO) was transcribed and translated in vitro. The import, targeting, and processing of the [35S]methionine-labeled precursor protein (pPPO) were studied in isolated chloroplasts. The protein was routed to the thylakoid lumen in two steps. The 67-kD precursor was first imported into the stroma in an ATP-dependent step. It was processed to a 62-kD intermediate by a stromal peptidase. Translocation into the lumen was light dependent and involved processing of the 62-kD to the 59-kD mature form. The mature polypeptide was soluble in the lumen and not bound to thylakoids. This two-step targeting pattern was observed in plastids from a variety of plants including pea (Pisum sativum L.), tomato, and maize (Zea mays L.). The ratio between the intermediate and mature forms observed depended on the plant species, leaf age, growth conditions, and illumination regime to which the plants had been subjected. Cu2+ was not required for pPPO import or processing. Furthermore, low concentrations of Cu2+ (1-5 microM) markedly inhibited the first import step. Tentoxin specifically inhibited pPPO import, leaving the precursor bound to the envelope membrane. The two-step routing of pPPO into chloroplasts, typical of thylakoid lumen proteins, is consistent with the two-domain structure of the transit peptide and appears to be a feature of all plant PPO genes isolated so far. No evidence was found for unorthodox routing mechanisms, which have been suggested to be involved in the import of plant PPOs. The two-step routing may account for some of the multiplicity of PPO observed in vivo.
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PMID:Import, targeting, and processing of a plant polyphenol oxidase. 797 97

Hair is actively pigmented only when it grows: the melanogenic activity of follicular melanocytes (MC) is strictly coupled to the anagen stage of the hair cycle. In catagen, melanin formation is switched off and is absent throughout telogen. The appearance of pigmentation is preceded, and further accompanied by, a time-frame - restricted, differential pattern of tyrosinase transcription, translation, and enzyme activities during the development of anagen follicles. In this speculative review, we argue that signals required for melanin synthesis and pigment transfer to bulb keratinocytes (KC) are intrinsic to the skin, rather than coming from the serum. First, the proopiomelanocortin (POMC) gene is expressed and translated during anagen, but is below the level of detectability in telogen; POMC is a precursor protein for adrenocorticotropin and melanotropins, which are potent regulators of MC proliferation and differentiation. Second, fibroblasts and KC produce factors that affect MC proliferation and differentiation. We suggest that signals regulating follicular MC activity partially derive from cutaneous cells expressing POMC. Vice versa, MC transfer to surrounding KC pigment granules with potent bioregulatory properties. MC also produce and secrete various signal molecules that can regulate mesenchymal and epithelial cell functions. Anagen-associated melanogenesis and the cyclic production of a pigmented hair shaft result from programmed and tightly coordinated epithelial-mesenchymal-neuroectodermal interactions, in which MC may act not only as pigmentary, but also as hair growth-regulatory cells.
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PMID:Melanogenesis is coupled to murine anagen: toward new concepts for the role of melanocytes and the regulation of melanogenesis in hair growth. 832 58

It is proposed that the phenol oxidase enzyme of schistosomes and other trematodes has a crucial role in the cross-linking of precursor proteins in the formation of the eggshell. However, to date there is no direct evidence to show that the enzyme catalyzes the reactions necessary for the posttranslational modification of eggshell precursor proteins. In this report we demonstrate that an eggshell precursor protein acts as a substrate for a schistosome fraction that catalyzed the 2 steps in the oxidation of tyrosine. This action of the phenol oxidase-containing worm fraction resulted in the tyrosine-dependent insolubilization and aggregation of the protein, suggesting a role for the enzyme in the posttranslational modification and cross-linking of schistosome eggshell proteins. The enzyme-rich fraction from Schistosoma mansoni catalyzed both steps of the reactions necessary for the conversion of tyrosine residues on putative eggshell precursor protein (p48) to quinones. The parasite fraction also catalyzed the hydroxylation of free L-tyrosine to DOPA (monophenol oxidase activity) and the oxidation of L-DOPA to dopaquinone (diphenol oxidase activity). Both activities of the enzyme are avidly bound to membranous structures, are susceptible to agents known to inhibit a functionally related enzyme, tyrosinase, and may reside on the same protein.
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PMID:Characteristics of phenol oxidase of Schistosoma mansoni and its functional implications in eggshell synthesis. 850 88

Two PCR-amplified genomic DNA fragments encoding apple (cv. Fuji) polyphenol oxidase (PPO) were cloned and sequenced. A comparison of genomic DNA with cDNAs revealed that the PPOs lacked introns. Both PPO DNAs appear to encode a 66-kDa precursor protein consisting of a 56-kDa mature protein and a N-terminal transit peptide of 10-kDa N-terminal transit peptide. Apple PPO DNA was expressed in Escherichia coli, and the gene product (56 kDa) without a transit peptide was immunochemically detected and was the same size (ca. 65 kDa) as the main PPO of apple fruit by SDS-PAGE.
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PMID:Cloning genomic DNA encoding apple polyphenol oxidase and comparison of the gene product in Escherichia coli and in apple. 953 95

Bruce's Sport is a mutant grapevine (Vitis vinifera L.) with green and white variegated fruit derived from the Sultana variety. The white regions of tissue have decreased polyphenol oxidase (PPO) activity resulting in a reduced capacity for browning. Active PPO from Sultana grapes was purified and had an apparent molecular weight of 40,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Western blots indicated that mature Sultana grapes contained a single 40-kilodalton PPO, and young Sultana berries also had small quantities of a 60-kilodalton protein. Bruce's Sport grapes had much less of the 40-kilodalton PPO and greater amounts of the 60-kilodalton band. Protease digestion of Bruce's Sport extracts decreased the proportion of the 60-kilodalton protein and increased the 40-kilodalton band. A cDNA clone of grape PPO was used to probe a northern blot of Sultana and Bruce's Sport RNA and hybridized to a 2.2-kilobase transcript in both grapevines. The level of PPO mRNA was high in the early stages of berry development but then declined. The results suggest that in grapevine the active 40-kilodalton form of PPO is synthesized as a precursor protein of at least 60 kilodaltons, and normal processing is interrupted in Bruce's Sport resulting in the accumulation of the 60-kilodalton inactive preform of PPO.
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PMID:Aberrant processing of polyphenol oxidase in a variegated grapevine mutant. 1666 82

Sprouting regulation in potato tubers is important for improving commercial value and producing new plants. Camphor shows flexible inhibition of tuber sprouting and prolongs the storage period of potato, but its underlying mechanism remains unknown. The results of the present study suggest that camphor inhibition caused bud growth deformities and necrosis, but after moving to more ventilated conditions, new sprouts grew from the bud eye of the tuber. Subsequently, the sucrose and fructose contents as well as polyphenol oxidase (PPO) activity were assessed after camphor inhibition. Transcription and proteomics data from dormancy (D), sprouting (S), camphor inhibition (C), and recovery sprouting (R) samples showed changes in the expression levels of approximately 4000 transcripts, and 700 proteins showed different abundances. KEGG (Kyoto encyclopaedia of genes and genomes) pathway analysis of the transcription levels indicated that phytohormone synthesis and signal transduction play important roles in tuber sprouting. Camphor inhibited these processes, particularly for gibberellic acid, brassinosteroids, and ethylene, leading to dysregulation of physiological processes such as cutin, suberine and wax biosynthesis, fatty acid elongation, phenylpropanoid biosynthesis, and starch and sucrose metabolism, resulting in bud necrosis and prolonged storage periods. The KEGG pathway correlation between transcripts and proteins revealed that terpenoid backbone biosynthesis and plant-pathogen interaction pathways showed significant differences in D vs. S samples, but 13 pathways were remarkably different in the D vs. C groups, as camphor inhibition significantly increased both the transcription levels and protein abundance of pathogenesis-related protein PR-10a (or STH-2), the pathogenesis-related P2-like precursor protein, and the kirola-like protein as compared to sprouting. In recovery sprouting, these genes and proteins were decreased at both the transcriptional level and in protein abundance. It was important to find that the inhibitory effect of camphor on potato tuber sprout was reversible, revealing the action mechanism was similar to resistance to pathogen infection. The present study provides a theoretical basis for the application of camphor in prolonging seed potato storage.
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PMID:Comparative Morphology, Transcription, and Proteomics Study Revealing the Key Molecular Mechanism of Camphor on the Potato Tuber Sprouting Effect. 2908 78