A ninhydrin-orthophthalaldehyde reagent for the determination of Ntau-methylhistidine

Derivatization of posttranslationally modified amino acids

After a brief overview of posttranslational modifications of protein amino acids, the use of various derivatizing reagents for amino acid analysis is discussed. Derivatization and chromatographic separation of hydroxyproline, methylhistidine, and phosphorylated amino acids are discussed in detail to illustrate some of the strategies that can be applied to the analysis of posttranslationally modified amino acids.

Analytical determination of methylated histidine in proteins: actin methylation

The methylation of histidine in actin from various muscle and nonmuscle sources has been studied by formation of phenylthiocarbamyl derivatives and subsequent reverse-phase high-pressure liquid chromatographic separation and analysis of actin hydrolyzates. All the actin species examined were found to contain 3-methylhistidine. This method has also been used in assays for the enzyme(s) responsible for methylation of rabbit skeletal muscle actin and to investigate the formation of other methylated residues in vitro. 3-Methyl-histidine is the major methylation product in this in vitro reaction.

Synergism of triiodothyronine and corticosterone on muscle protein breakdown

The concerted effect of triiodothyronine (T3) and corticosterone on muscle protein synthesis and breakdown was studied. Thyroidectomized young male rats were treated with T3 (1.5 microgram/100 g body weight per day), corticosterone (10 mg/100 g body weight per day) and both T3 and corticosterone for 4 days. On the 3rd day of the experiment urine was collected to measure N tau-methylhistidine excretion as an index of muscle protein breakdown. On the last day of the experiment, the rates of protein synthesis in skeletal muscles were measured by the large-dose [3H]phenylalanine method. N tau-Methylhistidine excretion was slightly increased by T3 treatment and it was increased about 3-times by corticosterone treatment. When both T3 and corticosterone were administered, it was increased about 6-fold. The rate of muscle protein breakdown calculated from the difference between the rate of protein synthesis and the growth rate was consistent with these findings. The rate of muscle protein synthesis was increased by T3, and it was decreased by corticosterone. The rate was the same as that of the thyroidectomized control group when the animals were given T3 and corticosterone, showing that T3 restrained the inhibiting effect of corticosterone on muscle protein synthesis. The results indicate that a physiological level of T3 enhances the catabolic action of pharmacological doses of glucocorticoids on muscle protein breakdown.

Measurement of urinary 3-methylhistidine with cationic-exchange resin

A simple method is presented for measurement of urinary 3-methylhistidine (3MH) using a cationic exchange resin treatment followed by colorimetric analysis. Equations are given to correct for the interference by histidine (4.3% by mole) in the colorimetric analysis. This correction is especially important for measurement of urinary 3MH in pregnant women or in other subjects with elevated histidine excretion. Good recovery of added standard and good reproducibility of results are documented. Preliminary data from a study of pregnant women are reported, suggesting an increased excretion of 3MH during pregnancy. Large day-to-day variability of 3MH excretion was observed within subjects. It is recommended that repeated measurements be done on each subject when determining 3MH excretion.

Genetic studies on the muscle protein turnover rate of coturnix quail

The validation of the urinary excretion of N tau-methylhistidine (N tau-MH) by quail as an index of the muscle protein turnover rate was tested using the criterion of the rate of recovery of radioactivity in urine following an intraperitoneal dose of L-[3-14C] methylhistidine. A genetic study on muscle protein turnover in quail was conducted using three genetically diverse lines (LL, large body size; SS, small body size; RR, random-bred control line) selected for body size. When L-[3-14C] methylhistidine was administered to 20-week-old male and female coturnix quail by direct intraperitoneal injection, approximately 90% of the L-[3-14C] methylhistidine was recovered by 96 hr postinjection. Recoveries were low in the egg and muscle. These results show that N tau-MH released from myofibrillar protein is not reutilized and the excretion of N tau-MH is a satisfactory index of muscle protein breakdown. In all lines, the amount of urinary N tau-MH excretion and fractional synthesis (Ks) and degradation (Kd) rates at the high growing period were higher than those at the low growing period. The Ks and Kd are significantly different among selected lines at both 3 and 6 weeks of age. At 3 weeks of age, the fractional rate of synthesis of the LL line (13.2%/day) was higher than that of the RR line (11.5%/day), whereas the SS (8.1%/day) was lower than that of the RR line (11.5%/day). The fractional rates of degradation of both the LL line (4.1%/day) and the SS line (5.6%/day) were lower than that of the RR line (7.0%/day) at 3 weeks of age. From these results, it was recognized that selection for body size gave rise to the changes in the muscle protein turnover rate.

The rate of degradation of myofibrillar proteins of skeletal muscle in broiler and layer chickens estimated by N tau-methylhistidine in excreta

After N tau-methylhistidine (N tau-MH) distribution among the various organs or the tissues was determined in male broiler chickens of 15 d of age, the rates of degradation of myofibrillar proteins in male layer and broiler chickens at different stages of growth were determined by means of N tau-MH. About 75 and 8% of the total N tau-MH in the tissues occurred respectively in skeletal muscle and stomach, and most of the remainder in the intestine and the skin. The rates of degradation of myofibrillar proteins in the male layer and broiler chickens of 21, 42 and 63 d of age were calculated to be 6.1, 4.5 and 2.4%/d (layer) and 5.0, 2.8 and 0.9%/d (broiler) respectively. These calculations involve the assumption that 80% of the total excreted N tau-MH was derived from skeletal muscle. The results strongly indicate that the rapid growth of the broiler chicken is facilitated by the reduced rate of protein degradation.

Determination of histidine and 3-methylhistidine in physiological fluids by high-performance liquid chromatography

High-performance liquid chromatography based on pre-column derivatization of histidine and 3-methylhistidine with o-phthalaldehyde-mercaptoethanol has been used to determine these amino acids in small volumes of plasma and urine. The elution is performed in 45 min on a 5-micron Resolve C18 column by a multi-step gradient. The eluted analytes are measured with a fluorescence detector which provides detection limits of less than 1 pmol per 20-microliter injection. The correlation between concentration and the integrated area of amino acids gives a linear relationship between 10 and 150 pmol per injection. Some preliminary results from patients with chronic renal failure under variation of diet are presented.

Variation among chicken stocks in the fractional rates of muscle protein synthesis and degradation

Fractional rates (% X day-1) of synthesis and degradation were determined by measuring the output of N tau-methylhistidine (MeHis) in the excreta at 4 and 8 weeks of age in the chicken. At 4 weeks of age, the fractional rate of synthesis of the meat-type stock was twice that of the egg-type stock (White Leghorn), but the fractional rates of synthesis at 8 weeks of age were similar (4.1-5.1% X day-1) among stocks. The fractional rate of degradation (1.3-1.5% X day-1) of the meat-type stock at 8 weeks of age was less than half the rate of the egg-type stock (2.9% X day-1). The fractional rates of synthesis and degradation at 4 weeks of age in the Satsuma native fowl were relatively high compared with those in the other stocks. In particular, the rate of degradation (8.6% X day-1) at 4 weeks of age was approximately twice that of other stocks. These results show that fractional rates of synthesis and degradation of muscle protein in the chicken differ among genetically diverse groups. The effect of changes in rates of synthesis and degradation on the change in fractional growth rate also differed. From regression coefficients (bks . FGR and bKd . FGR) of these rates in skeletal muscle protein on the fractional growth rate, it was recognized that the change in growth rate accompanies the changes in both synthesis and degradation in White Leghorn and commercial broilers but only the change in synthesis in White Plymouth Rock (dw) and Satsuma native fowl.

Effect of exercise on protein degradation: 3-methylhistidine and creatinine excretion

The effect of 1 hr of intensive exercise per day on protein breakdown was studied in a group of young male volunteers (20-25 years old) who were on a meat-free diet during the entire period of the study. Urinary 3-methylhistidine and creatinine were estimated as index of protein degradation. When studied over a period of 24 hr at different time points, the mean rates of 3-methylhistidine excretion were 2.4 and 2.9 nmole/min/kg for the day of exercise and nonexercise, respectively. Immediately following the exercise period, 3-methylhistidine and creatinine excretion rates decreased significantly.

A practical and reliable method for determination of urinary 3-methylhistidine

A practical and reliable semiautomated method for analysis of urinary 3-methylhistidine (3-MH) was designed combining the isolation of 3-MH by ion-exchange chromatography with the color reaction given by ninhydrin-orthopthalaldehyde (ninhydrin-OPT) reagent after alkalinization. 2 ml of urine were passed through disposable columns packed with an ion-exchange resin (Dowex 50-X8, 200-400 mesh) and the acidic and neutral amino acids were eluted with 10 ml of 0.2 M pyridine solution. Then, the 3-MH was quantitatively eluted and separated from histidine with a volume of 9 ml of a 1.5 M pyridine solution. Standard Autoanalyzer equipment was used for the automation of spectrophotometry. The method permits the analysis of 40 samples in duplicate per day. The 3-MH color reaction was linear for concentrations from 0.015 to 0.24 mu mol/ml. The mean recoveries of 3-MH from standards and urine were 98.6 +/- 1.3 and 99.0 +/- 1.3%, respectively. Duplicate determinations of urine samples showed a variation coefficient of 1.8%. An excellent agreement was obtained between urine samples analyzed by the present method and by an amino acid analyzer. The need for the elimination of the interfering amino acids was clearly demonstrated.