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.

In order to study the structure and function of a protein, it is generally required that the protein in question is purified away from all others. For soluble proteins, this process is greatly aided by the lack of any restriction on the free and independent diffusion of individual protein particles in three dimensions. This is not the case for membrane proteins, as the membrane itself forms a continuum that joins the proteins within the membrane with one another. It is therefore essential that the membrane is disrupted in order to allow separation and hence purification of membrane proteins. In the present review, we examine recent advances in the methods employed to separate membrane proteins before purification. These approaches move away from solubilization methods based on the use of small surfactants, which have been shown to suffer from significant practical problems. Instead, the present review focuses on methods that stem from the field of nanotechnology and use a range of reagents that fragment the membrane into nanometre-scale particles containing the protein complete with the local membrane environment. In particular, we examine a method employing the amphipathic polymer poly(styrene-co-maleic acid), which is able to reversibly encapsulate the membrane protein in a 10 nm disc-like structure ideally suited to purification and further biochemical study.

The synthesis of essential amino acids by the gut microflora of pigs, and their absorption, were assessed from the incorporation of (15)N from dietary (15)NH(4)Cl and of (14)C from dietary (14)C-polyglucose into amino acids in the body tissues of four pigs. Both (15)N and (14)C were incorporated into essential amino acids in body protein. Because pig tissues cannot incorporate (15)N into lysine or (14)C into essential amino acids, the labeling of these amino acids in body protein indicated their microbial origin. The absorption of microbial amino acids was estimated by multiplying the total content of each amino acid in the body by the ratio of the isotopic enrichment of the amino acid in the body to that in microbial protein. Because the ratio of (14)C:(15)N in body lysine was closer to that in the microflora of the ileum than to that of the cecum, absorption was assumed to take place exclusively in the ileum. The estimates of microbial amino acid absorption from (14)C-labeling were as follows (g/d): valine 1.8, isoleucine 0.8, leucine 2.0, phenylalanine 0.3 and lysine 0.9, whereas for lysine, the estimate from (15)N-labeling was 1.3 g/d. We conclude that the gastrointestinal microflora contribute significantly to the amino acid requirements of pigs.

1. Twenty-two British Friesian bull calves were used in a comparative slaughter experiment to determine the effects of a P-agonist (clenbuterol) on body composition and energy retention. Four calves were slaughtered at 18 d of age and constituted the initial slaughter group. Of the remaining calves, eight (group A, controls) were given milk replacer only, and ten calves (groups B and C, five calves per group) were given milk replacer plus clenbuterol(O.1 and 1.0 mg clenbuterol/kg milk replacer equivalent to approximately 2 and 20 pg/kg body-weight respectively over the 105k3 d of the experimental period). Calves were slaughtered over the weight range 146177 kg.2. Clenbuterol had no significant effect on dry matter (DM) intake, daily live-weight gain or feed conversion ratio. DM digestibility of the milk replacer was not affected by treatment. Nitrogen balance was measured on three separate occasions starting when the calves weighed approximately 60, 110 and 130 kg. N retention was increased over the experimental period in clenbuterol-treated calves, although the effect only achieved significance in calves weighing approximately 110 kg live weight (P < 0.05).3. Clenbuterol (20 pg/kg body-weight) increased estimated mean daily N retention in the carcass of the calves from 22 to 25 g whilst N retention in the non-carcass components decreased from 10 to 8 g/d. Effects of clenbuterol on N retention occurred mainly in skeletal muscle. Fat in both carcass and non-carcass components was reduced by treatment with clenbuterol. The total energy content of live-weight gain was reduced from 1077 to 897 MJ in clenbuterol-treated calves and mean daily heat production was estimated to increase from 23.1 in controls to 25.9 MJjd in calves in group C.4. In calves of mean live weight during balance of 120 and 136 kg, clenbuterol significantly increased daily urinary creatinine excretion and in 120 kg calves W-methylhistidine was significantly decreased (P < 0.05). Based on estimates of muscle mass from urinary creatinine and protein degradation from N7-methylhistidine excretion, the fractional breakdown rate of muscle protein in clenbuterol-treated calves was only 0.66 of that in the controls when the calves weighed 120 kg.Several reports Dalrymple et al. 1984;Ricks et al. 1984;Jones et al. 1985;Moser et al. 1986) have identified that the ,!I-adrenergic agonists clenbuterol (benzyl alcohol, 4-amino-R-(t-butyl-amino)methyl-3,5-dichloro) and cimaterol (CL263,780), when added to the diet of steers, lambs, poultry and pigs, produce an increase in muscle and a decrease in fat accretion which have been attributed to a shift in nutrient partitioning. From chemical analysis of the 9th to I Ith rib sections it was estimated that carcass protein in clenbuterol-treated steers was 1.15 and carcass fat 0.75 of that in controls . Estimation of body composition from rib analysis in animals treated with clenbuterol assumes that relations between rib composition and body composition which were obtained using untreated animals are the same for trea...

I . The recoveries of radioactivity in cattle urine following the intravenous administration of Nr-[14CHJmethyl histidine were essentially quantitative in 5-7 d in non-lactating cows, bulls and steers and did not change with age.2. The Nr-methyl histidine was excreted unchanged in urine. 3. Nr-methyl histidine occurred in muscle extracts both in the free form and as a perchloric acid-soluble, acid-labile form which accounted for approximately 85% of the total non-protein-bound Nr-methyl histidine in muscle and appeared identical to a similar component identified in muscle extracts of sheep and pigs.4. There was probably an age-related decrease in the concentration of the acid-labile component in muscle but which did not produce a measurable change in recovery of radioactivity in urine. 5.The daily excretion of "-methyl histidine (E, pmol) by male cattle was highly correlated with live weight (W, kg) by the equation:The excretions progressively decreased from 4.04 pmol/d per kg at 100 kg weight to 3.62 pmol/d per kg at 600 kg.6. By the criterion of the rate of clearance of labelled "-methyl histidine from the body, the excretion of Nr-methyl histidine in urine appears to be a valid index of muscle protein breakdown in cattle.