Creatine Phosphate

Creatine phosphate, or phosphocreatine (PCr), is a phosphorylated creatine molecule that acts as a rapidly mobilizable reserve of high-energy phosphates in skeletal muscle and brain: creatine phosphate can anaerobically donate a phosphate group to ADP to form adenosine triphosphate (ATP) during the first 2 to 7 seconds following an intense muscular or neuronal effort. On the converse, excess ATP can be used during a period of low effort to convert creatine to phosphocreatine. The reversible phosphorylation of creatine is catalyzed by several creatine kinases. The presence of creatine kinase (CK-MB, MB for muscle/brain) in plasma is indicative of tissue damage and is used in the diagnosis of myocardial infarction. The cell's ability to generate phosphocreatine from excess ATP during rest, as well as its use of phosphocreatine for quick regeneration of ATP during intense activity, provides a spatial and temporal buffer of ATP concentration. In other words, creatine phosphate acts as high-energy reserve in a coupled reaction; the energy given off from donating the phosphate group is used to regenerate the other compound - in this case, ATP. Creatine phosphate plays a particularly important role in tissues that have high, fluctuating energy demands such as muscle and brain.

Phosphocreatine is formed from parts of three amino acids: Arginine (Arg), Glycine (Gly), and Methionine (Met). It can be synthesized by formation of guanidinoacetate from Arg and Gly (in kidney) followed by methylation (S-adenosyl methionine, SAM is required) to creatine (in liver), and phosphorylation by creatine kinase (ATP is required) to phosphocreatine (in muscle); catabolism: hydrolysis to creatinine. Phosphocreatine is synthesized in the liver and transported to the muscle cells, via the bloodstream, for storage. Creatine phosphate shuttle help transport of high energy phosphate from mitochondria.

Heme

Heme is a molecule that is synthesized by the sequential actions of eight enzymes and is everywhere in nature. A heme is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are known as hemoproteins. As a prosthetic group, heme mediates reversible binding of oxygen by hemoglobin.

The heme synthesis begins in the mitochondria and continues in the cytoplasm. The process begins in the mitochondria because one of the precursors is found only there. Since this reaction is regulated in part by the concentration of heme, the final step which produces the heme is mitochondrial. Most of the intermediate steps are cytoplasmic. Heme is also catabolized to yield biliverdin, one atom of iron, and one molecule of carbon monoxide and is subsequently reduced to bilirubin.

There are several biologically important kinds of heme; the most common type is heme B; other important types include heme A and heme C. Isolated hemes are commonly designated by capital letters while hemes bound to proteins are designated by lower case letters.

Porphyrins

Porphyrins are a group of organic compounds that occur in nature, specially as the pigment in red blood cells. They are cyclic macromolecules called macrocycles that are characterized by the presence of four modified pyrrole subunits interconnected at their a carbon atoms via methine bridges (=CH-). Porphyrins are aromatic, and they obey Hückel's rule for aromaticity in that they possess 4n+2 pi electrons that are delocalized over the macrocycle. The macrocycles, therefore, are highly-conjugated system and consequently are deeply colored - the name porphyrin comes from a Greek word for purple. The macrocycle has 26 pi electrons. The parent porphyrin is porphine, and substituted porphines are called porphyrins.

Heavy Water

Heavy water is chemically the same as regular water, but with the two hydrogen atoms (as in H2O) replaced with heavy hydrogen atoms called deuterium, hence the symbol D2O of heavy water. Deuterium is an isotope of hydrogen and it has one extra neutron. Thus the deuterium atom consists of one proton and one neutron in the atomic nucleus with one electron orbiting around. It is the extra neutron that makes heavy water "heavy", about 10% heavier in fact.

Hydrogen / Deuterium / Tritium

Ordinary water / Heavy water

Chemistry

Chemistry is the science which deals with the composition, melecular and atomic structure, and properties of substances and with the transformation that they undergo. Modern chemistry evolved out of alchemy, which had been practiced for several centuries in various parts of the world, particularly during the Middle Ages, when scholars in those days thought that they could transform cheaper metals into gold. Chemistry is often called the central science because it connects the other natural sciences, such as astronomy, physics, biology, and geology.

The influences of philosophers such as Sir Francis Bacon (1561-1626) and Rene Descartes (1596-1650), who demanded more rigor in mathematics and in removing bias from scientific observations, led to a scientific revolution. In chemistry, this began with Robert Boyle (1627-1691), who came up with an equations known as the Boyle's Law about the characteristics of gaseous state. Chemistry indeed came of age when Antoine Lavoisier (1743-1794), developed the theory of Conservation of mass in 1783, and the development of the Atomic Theory by John Dalton around 1800. The Law of Conservation of Mass resulted in the reformulation of chemistry based on this law and the oxygen theory of combustion, which was largely based on the work of Lavoisier.