Guanine (2-amino-6-oxypurine) is one of the four main nitrogenous bases found in nucleic acids (e.g., DNA and RNA). Guanine is a purine derivative and in Watson-Crick base pairing forms hydrogen bonds with cytosine. The nucleoside is called guanosine. Guanine is also the name of a white amorphous substance found in the scales of certain fishes, the guano of sea-birds, and the liver and pancreas of mammals.
Guanine is a purine base found in DNA and RNA. In nucleosides and nucleotides, guanine is linked to the sugar moiety via a covalent bond between nitrogen #9 of guanine and carbon #1 of the sugar. The ribonucleoside containing guanine is called guanosine. The deoxyribonucleoside containing guanine is called deoxyguanosine. In cells it usually occurs condensed with ribose or deoxyribose to form the nucleosides guanosine and deoxyguanosine. It is one of the four bases in DNA that make up the letters ATGC, guanine is the "G". The others are adenine, cytosine, and thymine. Guanine always pairs with cytosine.
Guanine nucleotide binding proteins are glycoproteins anchored on the cytoplasmic cell membrane. They are mediators for many cellular processes, including signal transduction, protein transport, growth regulation and polypeptide chain elongation. They are also known as GTP-binding proteins and GTPases. Almost all members of this superfamily of proteins act as molecular switch, which is on when GTP is bound and off when GDP is bound. Binding is specific for the guanine base, with affinity of the order of 1011-1012 M-1 for GDP and GTP, whilst binding affinity for GMP and other nucleotide bases are 6 orders less.
The activity of guanine nucleotide binding proteins is dependent on divalent ions, which is Mg++ in vivo. Mg++ forms octahedral coordinate bonds. When GTP is bound, two neighbouring equatorial dative bonds are connected to 2 oxygen atoms of the beta and gamma phosphates of GTP, whilst the other two equatorial bonds are connected to the hydroxyl oxygen of Ser17 and Thr35, respectively. Both polar dative bonds are linked to water molecules. When GDP is bound, the coordinately bonded oxygen of gamma phosphate is replaced by a water molecule. The hydroxyl oxygen of Thr35 is also broken off and replaced by a water molecule.
Synonyms: 2-aminohypoxanthine, guanin, guanine enol, C.I. 75170, C.I. natural white 1, natural pearl essence, dew pearl, stella polaris, 2-amino-1,7-dihydro-6H-purin-6-one, naturon, mearlmaid
Molecular formula: C5H5N5O
CAS No: 73-40-5