Question

viral transformation phosphorous
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Answer 1

Answer:

Tyrosine protein kinases carry out a newly described form of protein modification – phosphorylation of tyrosine residues. The transforming proteins of certain tumor viruses are tyrosine protein kinases and unscheduled phosphorylation of tyrosine in cellular proteins appears to be crucial for malignant transformation by these viruses. A primary effect of two cellular growth factors is to activate intracellular tyrosine protein kinases.

A new type of protein modification which appears to be involved in a number of crucial metabolic processes has been recognized only in the past 2 years. Phosphotyrosine had not been detected as a constituent of proteins until the discovery that the amino acid phosphorylated by certain viral transforming proteins was tyrosine1–3. Previously, the only acid stable phosphoamino acids known in proteins were phosphoserine and phosphothreonine. The failure to observe phosphotyrosine stemmed in part from the dearth of this modified amino acid in normal cells. Phosphotyrosine accounts for only about 0.05% of the total acid-stable phosphate in protein in animal cells4. Nevertheless, despite the scarcity of phosphotyrosine, evidence is accumulating that tyrosine-specific protein kinases may be an important class of regulatory enzymes.