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Biomedical subjects

C I Harris

Publications and source records attributed to C I Harris.

36 records · Page 2Linked to original sources
PubMed1980

The urinary excretion of N tau-methyl histidine in sheep: an invalid index of muscle protein breakdown.

1. The validity of the urinary excretion of N tau-methyl histidine (N tau-MH) in sheep as a measure of the breakdown of muscle protein in vivo was assessed from the urinary recovery of radioactivity following the intravenous administration of N tau-[14CH3]methyl histidine. 2. Recoveries of radioactivity in urine from animals of 4 weeks to 7 years of age were incomplete in 7 d but progressively increased with the age of the animal, becoming almost quantitative (90%) in older animals after recovery for 3 weeks. 3. The incomplete urinary recoveries were not due to partial excretion of N tau-MH in faeces or its oxidation and elimination in expired gases but were related to the presence in muscle of a pool of non-protein-bound N tau-MH which was several times larger than the expected daily urinary excretion. 4. This pool in newly accreted muscle tissue was maintained by retention of some of the N tau-MH released by breakdown of muscle protein. Hence, only a proportion of the N tau-MH released from protein breakdown was available for excretion. This proportion increased with the age of the animal and was probably the main determinant of the improved recoveries of radioactivity obtained in urine from older animals. 5. The non-protein-bound N tau-MH in muscle consisted of free N tau-MH and a dipeptide containing N tau-MH, the latter comprising on average approximately 82% of the total non-protein-bound N tau-MH in muscle. This proportion did not change appreciably with the age of the animal. 6. The dipeptide appeared to be synthesized in muscle from free N tau-MH and was not a terminal product of protein breakdown. 7. The results show that urinary excretion of N tau-MH is not a reliable index of muscle protein breakdown in sheep.

Age Factors↗
PubMed1977

Use of the constant infusion technique for measuring rates of protein synthesis in the New Zealand White rabbit.

1. To study the potential of the constant-infusion technique for measuring rates of protein synthesis in New Zealand White rabbits, animals were infused for up to 6 h with radioactively-labelled tyrosine. 2. Labelled tyrosine from plasma and tissues was isolate from labelled metabolites by ion-exchange chromatography. 3. Analysis of serial blood and muscle biopsy samples removed under anaesthesia showed that the specific radioactivity (SR) of the free tyrosine pools reached an approximately constant value within 2 h. 4. Certain commercial preparations of L-[side-chain 2,3-3H]tyrosine were contaminated with 300 mg radioactive D-tyrosine/g. The D-isomer appeared to enter the muscle intracellular pool. 5. In constant-infusion experiments L-[3H]tyrosine could replace the uniformly-14C-labelled L-isomer for the determination of rates of protein synthesis in muscle. L-[side-chain 2,3-3H]tyrosine may not be suitable for use as a precursor for measuring rates of liver protein synthesis. 6. Evidence is presented that the precursor of liver protein synthesis may not be well defined by the SR for free tyrosine of the homogenate. 7. The technique was used to measure the rates of protein synthesis in adult rabbits. The rates of protein synthesis in liver and muscle were measured and from measurements of tyrosine flux the mean rate of whole-body protein synthesis was calculated as 13-8 g/kg per d.

Animals↗
PubMed1976

Amino acid sequence of penicillopepsin. III. Isolation and characterization of amino terminal, tryptic, and tryptophanyl peptides.

The amino acid sequence of peptides isolated from a tryptic digest of penicillopepsin (EC 3.4.23.7), a subtilisin (EC 3.4.21.14) digest of maleylated penicillopepsin, and a chymotryptic digest of penicillopepsin modified with dinitrophenylsulfenyl (DNPS) chloride have been determined. The first two digests identified four of the five lysyl residues of the enzyme as well as the N-terminal peptide. The third digest provided overlaps at three of the tryptophanyl residues. The DNPS-tryptophan peptides were isolated on an affinity column prepared by coupling dinitrophenyl antibody raised in sheep to cyanogen bromide-activated Sepharose.

Amino Acid Sequence↗
PubMed1976

Amino acid sequence of penicillopepsin. IV. Myxobacter AL-1 protease II and Staphylococcus aureus protease fragments and homology with pig pepsin and chymosin.

The digest of penicillopepsin (EC 3.4.23.7) with protease II from Myxobacter AL-1 gave five fragments which were separated on a Biogel P-100 column in 70% formic acid. The fragments were from 16 to 125 amino acids long. Two fragments were also isolated from a digest with a protease from Staphylococcus aureus. The analysis of these fragments by automatic sequencer gave a number of overlaps of the chymotryptic and thermolytic peptides. The available amino acid sequence data for penicillopepsin described in this paper and the accompanying papers (Kurosky, A. and Hofmann, T.:Can. J. Biochem. 54, 872 (1976);Rao, L and Hofmann, T.:Can. J. Biochem.54,885 (1976); Harris, C.I.,Rao, L., Shutsa, P., Kurosky, A. and Hofmann, T.: Can. J. Biochem. 54,895 (1976) have been combined and yield 15 fragments which range in lengths from 3 to 112 amino acid residues. These unique fragments account for virtually all the amino acids of the fungal protease. Four of the fragments with a total of 194 residues (about 60% of the molecule) have been aligned with corresponding sections of pig pepsin (EC 3.4.23.1) and with part of the N-terminal sequence available for calf chymosin (EC 3.4.23.4). In the alignments about 37% of the residues in the fungal enzyme are identical with at least one of the mammalian enzymes. An additional 20% are chemically similar. These results, together with previously reported active site directed modifications, show conclusively that penicillopepsin is an evolutionary homologue of the mammalian acid proteases.

Amino Acid Sequence↗
PubMed1970

Occurrence and formation of the N epsilon-methyl-lysines in myosin and the myofibrillar proteins.

1. Adult rabbit skeletal-muscle myosin has been shown to contain 1.0 residue of mono-N(in)-methyl-lysine and 3.3 residues of tri-N(in)-methyl-lysine per molecule of molecular weight 500000. 2. The methyl-lysines appear to be located in the subfragment 1 portion of the myosin molecule. 3. Methyl-lysines are not present in actin, tropomyosin, inhibitory factor and calcium-sensitizing factor. 4. Enzymic methylation of histidine and lysine residues of myosin has been demonstrated in vitro. 5. The methylation of histidine and lysine of the total myofibrillar protein occurs after peptide-bond synthesis. 6. Although methylated lysines and 3-methyl-histidine could not be detected by analysis of hydrolysates, radiochemical evidence is provided for the presence of these residues in the soluble-protein fraction of rabbit skeletal muscle.

Amino Acids↗
PubMed1967

3-methylhistidine in actin and other muscle proteins.

1. By the use of the extended elution system for basic amino acid analysis, 3-methylhistidine has been detected in hydrolysates of actin isolated from mammalian, fish and bird skeletal muscle. 2. Evidence is presented to indicate that 3-methylhistidine forms part of the primary structure and that in rabbit actin this residue is restricted to one peptide fraction obtained from the tryptic digest. 3. Rabbit skeletal-muscle actin has a 3-methylhistidine:histidine ratio 1:7.6, indicating a minimum molecular weight of 47600. 4. Adult rabbit myosin contains approximately 2 3-methylhistidine residues/mol. These residues are localized in the heavy meromyosin part of the molecule, and are restricted to the major component obtained after succinylation.

Amino Acids↗
PubMedDate not supplied

Arginine metabolism in benign and malignant disease of breast and colon: evidence for possible inhibition of tumor-infiltrating macrophages.

L-Arginine concentrations have been measured in benign and malignant breast and colonic neoplasms and compared with the macrophage content and arginase activity within these tumors. Our study confirmed previous findings of elevated plasma arginine concentrations in malignancy and demonstrated that tissue free-arginine concentrations are substantially higher in malignant (mean 9.8 mumol/g protein) than benign (2.8 mumol/g protein) breast disease. Similarly, malignant colonic neoplasms had a higher free-arginine concentration than benign colonic polyps (14.0 vs. 7.0 mumol/g protein). The macrophage content of the malignant tumors was also significantly higher than in the benign conditions (278 vs 29/high power field in breast disease), but despite this, there was no detectable difference in the arginase activity. These findings suggest that tumor-infiltrating macrophages are not able to produce this enzyme, and/or its activity is inhibited within the tumor cell milieu. The differences observed in the arginine concentrations within these lesions has potentially important implications for the pathway of arginine metabolism and local host antitumor responses.

Arginase↗