Thermolabile: Any substance, but especially biochemical substances, that change dramatically, decompose, or are destroyed by heat of 55 degrees Celsius or greater.  

Aldehyde: Any one of  a class of very reactive organic chemical compounds obtained by oxidation of primary alcohols, characterized by a carbon atom double-bonded to an oxygen, single-bonded to a hydrogen, and single-bonded to another chemical group.

Isomer: Chemical substances composed of identical elements in identical proportions,  but which differ in properties because of differences atomic structure.

Protein Moiety: The protein portion of the structure of a molecule.

All-trans-configuration: The orange retinaldehyde resulting from the action of light on the rhodopsin of the retina, which converts the 11-cis-retinal component of the rhodopsin to all-trans-retinal plus opsin.

G protein: any of a family of similar heterotrimeric proteins of the intracellular portion of the plasma membrane that bind activated receptor complexes and, through conformational changes and cyclic binding and hydrolysis of GTP, directly or indirectly effect alterations in channel gating and so couple cell surface receptors to intracellular responses. Some G proteins are named for their activities, e.g., Gs stimulates and Gi inhibits enzyme activity.

guanosine triphosphate: (GTP) a nucleotide, the 5-triphosphate of guanosine; it is an activated precursor in the synthesis of ribonucleic acid and is also involved in energy metabolism, being produced from GDP by substrate level phosphorylation in the tricarboxylic acid (Krebs) cycle and serving as a source of free energy to drive protein synthesis. The ratio of GTP to ATP is maintained by the reversible transfer of phosphate catalyzed by GDP kinase.

guanosine diphosphate: (GDP) a nucleotide, the 5-pyrophosphate of guanosine, which serves as a carrier for mannose residues in glycoprotein synthesis and as a substrate for a phosphorylation reaction of the tricarboxylic acid cycle.

Phosphodiesterase: An enzyme that breaks a phosphodiester bond, for example, that which cleaves cAMP into AMP. 

ester: a compound formed by removal of water from an acid and an alcohol

hydrolysis: the splitting of a compound into fragments by the addition of water, the hydroxyl group being incorporated in one fragment, and the hydrogen atom in the other.

Glutamate: Glutimate is a salt, ester, or anionic form of glutamic acid, it is the major excitatory neurotransmitter in the mammalian brain.