Histidine is an α-amino acid, used in the biosynthesis of proteins. It contains an α-amino group, a carboxylic acid group, an imidazole side chain, classifying it as a positively charged amino acid at physiological pH. Thought essential only for infants, longer-term studies have shown it is essential for adults also, it is encoded by the codons CAU and CAC. Histidine was first isolated by German physician Albrecht Kossel and Sven Gustaf Hedin in 1896, it is a precursor to histamine, a vital inflammatory agent in immune responses. The acyl radical is histidyl; the conjugate acid of the imidazole side chain in histidine has a pKa of 6.0. Thus, at below a pH of 6, the imidazole ring is protonated; the resulting imidazolium ring has a positive charge. The positive charge is distributed between both nitrogens and can be represented with two important resonance structures. Above pH 6, one of the two protons is lost; the remaining proton of the imidazole ring can reside on either nitrogen, giving rise to what are known as the N1-H or N3-H tautomers.
The N3-H tautomer, shown in the figure above, is protonated on the #3 nitrogen, farther from the amino acid backbone bearing the amino and carboxyl groups, whereas the N1-H tautomer is protonated on the nitrogen nearer the backbone. The imidazole/imidazolium ring of histidine is aromatic at all pH values; the acid-base properties of the imidazole side chain are relevant to the catalytic mechanism of many enzymes. In catalytic triads, the basic nitrogen of histidine abstract a proton from serine, threonine, or cysteine to activate it as a nucleophile. In a histidine proton shuttle, histidine is used to shuttle protons, it can do this by abstracting a proton with its basic nitrogen to make a positively charged intermediate and use another molecule, a buffer, to extract the proton from its acidic nitrogen. In carbonic anhydrases, a histidine proton shuttle is utilized to shuttle protons away from a zinc-bound water molecule to regenerate the active form of the enzyme. In helices E and F of haemoglobin, histidine influences binding of dioxygen as well as carbon monoxide.
This interaction enhances the affinity of Fe for O2 but destabilizes the binding of CO, which binds only 200 times stronger in haemoglobin, compared to 20,000 times stronger in free haem. The tautomerism and acid-base properties of the imidazole side chain has been characterized by 15N NMR spectroscopy; the two 14N chemical shifts are similar. NMR spectral measurements shows that the chemical shift of N1-H drops whereas the chemical shift of N3-H drops considerably; this change indicates that the N1-H tautomer is preferred due to hydrogen bonding to the neighboring ammonium. The shielding at N3 is reduced due to the second-order paramagnetic effect, which involves a symmetry-allowed interaction between the nitrogen lone pair and the excited π* states of the aromatic ring. At pH > 9, the chemical shifts of N1 and N3 are 185 and 170 ppm. The imidazole sidechain of histidine serves as a ligand in metalloproteins. One example is the axial base attached to Fe in hemoglobin. L-Histidine, is an essential amino acid, not synthesized de novo in humans.
Humans and other animals must ingest histidine-containing proteins. The biosynthesis of histidine has been studied in prokaryotes such as E. coli. Histidine synthesis in E. coli involves eight gene products and it occurs in ten steps. This is possible. For example, as shown in the pathway, His4 catalyzes 4 different steps in the pathway. Histidine is synthesized from phosphoribosyl pyrophosphate, made from ribose-5-phosphate by ribose-phosphate diphosphokinase in the pentose phosphate pathway; the first reaction of histidine biosynthesis is the condensation of PRPP and adenosine triphosphate by the enzyme ATP-phosphoribosyl transferase. ATP-phosphoribosyl transferase is indicated by His1 in the image. His4 gene product hydrolyzes the product of the condensation, phosphoribosyl-ATP, producing phosphoribosyl-AMP, an irreversible step. His4 catalyzes the formation of phosphoribosylformiminoAICAR-phosphate, converted to phosphoribulosylformimino-AICAR-P by the His6 gene product. His7 splits phosphoribulosylformimino-AICAR-P to form d-erythro-imidazole-glycerol-phosphate.
After, His3 forms imidazole acetol-phosphate releasing water. His5 makes l-histidinol-phosphate, hydrolyzed by His2 making histidinol. His4 catalyzes the oxidation of l-histidinol to an amino aldehyde. In the last step, l-histidinal is converted to l-histidine. Just like animals and microorganisms, plants need histidine for their development. Microorganisms and plants are similar in. Both synthesize histidine from the biochemical intermediate phosphoribosyl pyrophosphate. In general, the histidine biosynthesis is similar in plants and microorganisms; this pathway requires energy in order to occur therefore, the presence of ATP activates the first enzyme of the pathway, ATP-phosphoribosyl transferase. ATP-phosphoribosyl transferase is the rate determining enz
Mike Harper is considered to be one of America's leading opinion makers on NASCAR and ARCA RE/MAX Series racing topics. His Spin Out Zone column was established in 2001 and has grown into one of the industry's most popular racing web sites. In 2007, he joined forces with digital media artist Lori Munro and NASCAR writer Dennis Michelsen in the purchase of RaceTalkRadio.com. The network has grown since 2007 from a web site hosting one Internet radio show to the nation's largest independent Internet radio network dedicated to racing. Racing programs include shows hosted by SPEED TV's Bob Dillner, XM Radio's Joe Castello and NASCAR Driver Greg Biffle. Shows include the SpeedFreaks and BAM Spirit. In addition to his work in racing media, Mike is a travel management industry veteran having worked with Fortune 500 corporations, small to mid-size companies and Universities on managing their travel programs. In 2007, Mike began hosting the only dedicated ARCA RE/MAX Series racing radio show in the nation called Inside the ARCA RE/MAX Series presented by Dale Jarrett Racing Adventure on RaceTalkRadio.com.
Show talent included Dennis Michelsen and Chris Knight. Today, the show has grown into one of the most successful racing programs in the industry. Supported by companies like Office Depot, GLOCK, CASITE, SPEED TV, AAA and Rockingham Speedway, the Thunder Crew airs on RaceTalkRadio.com every Tuesday night with some of the biggest names in NASCAR, ARCA and the racing media. Mike's racing updates have been heard on national networks like ESPN Radio. Local stations have picked up his updates including WHEELZ 104.5 FM in Mid-Michigan and 105.7 in Ohio. In print media, Mike's Spin Out Zone column has been featured in SpeedWorld Magazine. SpeedWorld is a worldwide publication owned by Synergy Publishing International, a diversified multi-media communications corporation headquartered in Clearwater, Florida, U. S. A; as a contributor, Mike's work has been published on SPEEDTV.com, ARCARacing.com, NASCAR industry's second largest media web site ThatsRacin.com, produced by The Charlotte Observer, owned by The McClatchy Company, the second-largest newspaper company in the United States.
Other newspaper contributions include The Hearst Corporation, one of the nation's largest diversified media companies. Its major interests include magazine and business publishing, cable networks and radio broadcasting, internet businesses, TV production and distribution, newspaper features distribution and real estate. Mike has interviewed many ARCA and NASCAR stars, television executives/personalities from ESPN, Fox Sports and Speed Channel, national personalities like wrestler/movie star Bill Goldberg and Commander in Chief of the United States Central Command from July 2000 through July 2003, General Tommy Franks. For most companies “travel & entertainment” costs represent the second highest controllable annual expense, exceeded only by salary & benefits. Corporate travel management is the function of managing a company's approach to travel by developing a travel policy, the negotiations with all vendors, day-today operation of the corporate travel program, traveller safety & security, credit-card management and T&E data management.
As a business-to-business professional, Mike has managed all aspects of the travel program including business development, account management and operations management. Mike was born and raised in Texas and has residences in Michigan and Texas with his wife and son, Tyler
Barnwell County is a county in the U. S. state of South Carolina. As of the 2010 census, its population was 22,621, its county seat is Barnwell. The Barnwell District was created in 1797 from the southwestern portion of the Orangeburg District, along the Savannah River, it was named after a local figure in the Revolutionary War. In 1868, under the South Carolina Constitution revised during Reconstruction, South Carolina districts became counties; the government was made more democratic, with county officials to be elected by male citizens at least 21 years old, rather than by the state legislature as done previously. In 1871 the legislature took the northwestern portion of the county to form part of the new Aiken County, the only county organized during the Reconstruction era. In 1874 the border with Aiken County was adjusted slightly; this county and Barnwell, with populations of blacks and whites that were nearly equal, had extensive violence in the months before the 1874 and 1876 elections, as groups of paramilitary Red Shirts rode to disrupt black Republican meetings and intimidate voters to suppress black voting.
More than 100 black men were killed in Aiken County during the violence at Ellenton, South Carolina. In 1895 white Democrats in the state legislature passed a new constitution, disfranchising most blacks for more than 60 years by raising barriers to voter registration. In 1897 the eastern third of the county was taken to form the new Bamberg County. In 1919 most of the southern half of the county was taken to form most of the new Allendale County, thus reducing Barnwell county to its present size. According to the U. S. Census Bureau, the county has a total area of 557 square miles, of which 548 square miles is land and 8.9 square miles is water. Aiken County - north Bamberg County - east Orangeburg County - east Allendale County - southeast Burke County, Georgia - southwest As of the census of 2000, there were 23,478 people, 9,021 households, 6,431 families living in the county; the population density was 43 people per square mile. There were 10,191 housing units at an average density of 19 per square mile.
The racial makeup of the county was 55.18% White, 42.55% Black or African American, 0.35% Native American, 0.39% Asian, 0.03% Pacific Islander, 0.78% from other races, 0.72% from two or more races. 1.39 % of the population were Latino of any race. There were 9,021 households out of which 34.80% had children under the age of 18 living with them, 47.40% were married couples living together, 19.30% had a female householder with no husband present, 28.70% were non-families. 25.60% of all households were made up of individuals and 10.20% had someone living alone, 65 years of age or older. The average household size was 2.57 and the average family size was 3.08. In the county, the population was spread out with 28.10% under the age of 18, 8.70% from 18 to 24, 27.90% from 25 to 44, 22.60% from 45 to 64, 12.60% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 92.70 males. For every 100 females age 18 and over, there were 86.50 males. The median income for a household in the county was $28,591, the median income for a family was $35,866.
Males had a median income of $31,161 versus $21,904 for females. The per capita income for the county was $15,870. About 17.90% of families and 20.90% of the population were below the poverty line, including 27.30% of those under age 18 and 24.40% of those age 65 or over. As of the 2010 United States Census, there were 22,621 people, 8,937 households, 6,055 families living in the county; the population density was 41.2 inhabitants per square mile. There were 10,484 housing units at an average density of 19.1 per square mile. The racial makeup of the county was 52.6% white, 44.3% black or African American, 0.6% Asian, 0.4% American Indian, 0.7% from other races, 1.5% from two or more races. Those of Hispanic or Latino origin made up 1.8% of the population. In terms of ancestry, 11.5% were American, 5.7% were German, 5.4% were English. Of the 8,937 households, 34.0% had children under the age of 18 living with them, 41.8% were married couples living together, 20.8% had a female householder with no husband present, 32.2% were non-families, 28.4% of all households were made up of individuals.
The average household size was 2.50 and the average family size was 3.05. The median age was 38.8 years. The median income for a household in the county was $33,816 and the median income for a family was $41,764. Males had a median income of $35,957 versus $30,291 for females; the per capita income for the county was $17,592. About 20.8% of families and 25.4% of the population were below the poverty line, including 39.6% of those under age 18 and 11.5% of those age 65 or over. Barnwell Blackville Elko Hilda Kline Snelling Williston Prior to 1948, Barnwell County was a Democratic Party stronghold similar to the rest of the Solid South, with Democratic presidential candidates receiving near-unanimous margins of victory in most years; the twenty years from 1948 to 1968 were a transitional time for the politics of South Carolina & Barnwell County in part due to the Democratic Party's increasing support for African-American civil rights & enfranchisement. Segregationist candidates Strom Thurmond & George Wallace won the county in those aforementioned years, bookended by Democratic wins in 1952 & 1956 & Republican wins in 1960 & 1964.
From 1972 on, the county has Republican, but has become more of a swing county in recent years, backing the national winner in every presidential election from 2000 on. Rosa Louise Woodberry, school founder National Register of Historic Places list