Question: Also known as spirit of nider, what reacts with proteins to form yellow products?

Nitric acid (HNO), also known as aqua fortis and spirit of niter, is a highly corrosive mineral acid. <SEP> Aspartic acid (abbreviated as Asp or D; encoded by the codons [GAU and GAC]), also known as aspartate, is an α-amino acid that is used in the biosynthesis of proteins.  Similar to all other amino acids it contains an amino group and a carboxylic acid.  Its α-amino group is in the protonated –NH form under physiological conditions, while its α-carboxylic acid group is deprotonated −COO under physiological conditions.  Aspartic acid has an acidic side chain (CHCOOH) which reacts with other amino acids, enzymes and proteins in the body.  Under physiological conditions (pH 7.4) in proteins the side chain usually occurs as the negatively charged aspartate form, −COO .  It is a non-essential amino acid in humans, meaning the body can synthesize it as needed. <SEP> Inhibitor of DNA-binding/differentiation proteins, also known as ID proteins comprise a family of proteins that heterodimerize with basic helix-loop-helix (bHLH) transcription factors to inhibit DNA binding of bHLH proteins.  ID proteins also contain the HLH-dimerization domain but lack the basic DNA-binding domain and thus regulate bHLH transcription factors when they heterodimermize with bHLH proteins.  The first helix-loop-helix proteins identified were named E-proteins because they bind to Ephrussi-box (E-box) sequences.  In normal development, E proteins form dimers with other bHLH transcription factors, allowing transcription to occur.  However, in cancerous phenotypes, ID proteins can regulate transcription by binding E proteins, so no dimers can be formed and transcription is inactive.  E proteins are members of the class I bHLH family and form dimers with bHLH proteins from class II to regulate transctiption.  Four ID proteins exist in humans: ID1, ID2, ID3, and ID4.  The ID homologue gene in Drosophila is called extramacrochaetae (EMC) and encodes a transcription factor of the helix-loop-helix family that lacks a DNA binding domain.  EMC regulates cell proliferation, formation of organs like the midgut, and wing development.  ID proteins could be potential targets for systemic cancer therapies without inhibiting the functioning of most normal cells because they are highly expressed in embryonic stem cells, but not in differentiated adult cells.  Evidence suggests that ID proteins are overexpressed in many types of cancer.  For example, ID1 is overexpressed in pancreatic, breast, and prostate cancers.  ID2 is upregulated in neuroblastoma, Ewing’s sarcoma, and squamous cell carcinoma of the head and neck. <SEP> Xanthoproteic acid is a noncrystallizable yellow substance derived from proteins upon treatment with nitric acid.  This reaction is known as the xanthoproteic reaction.  This test is carried out by adding concentrated nitric acid to the substance being tested, and then heating the mixture.  Nitric acid reacts with proteins to form yellow nitrated products.  If proteins are present that contains amino acids with aromatic rings, the mixture turns yellow.  Upon adding a strong base such as liquid ammonia, the color turns orange.  These color changes are caused by nitrated aromatic rings in the protein.  The xanthoproteic test is specific for aromatic compounds such as tyrosine, tryptophan and phenyalanine.