The hydrolysis of proteins

Dityrosine Crosslinking of Collagen and Amyloid-β Peptides Is Formed by Vitamin B12 Deficiency-Generated Oxidative Stress in Caenorhabditis elegans

(1) Background: Vitamin B12 deficiency in Caenorhabditis elegans results in severe oxidative stress and induces morphological abnormality in mutants due to disordered cuticle collagen biosynthesis. We clarified the underlying mechanism leading to such mutant worms due to vitamin B12 deficiency. (2) Results: The deficient worms exhibited decreased collagen levels of up to approximately 59% compared with the control. Although vitamin B12 deficiency did not affect the mRNA expression of prolyl 4-hydroxylase, which catalyzes the formation of 4-hydroxyproline involved in intercellular collagen biosynthesis, the level of ascorbic acid, a prolyl 4-hydroxylase coenzyme, was markedly decreased. Dityrosine crosslinking is involved in the extracellular maturation of worm collagen. The dityrosine level of collagen significantly increased in the deficient worms compared with the control. However, vitamin B12 deficiency hardly affected the mRNA expression levels of bli-3 and mlt-7, which are encoding crosslinking-related enzymes, suggesting that deficiency-induced oxidative stress leads to dityrosine crosslinking. Moreover, using GMC101 mutant worms that express the full-length human amyloid β, we found that vitamin B12 deficiency did not affect the gene and protein expressions of amyloid β but increased the formation of dityrosine crosslinking in the amyloid β protein. (3) Conclusions: Vitamin B12-deficient wild-type worms showed motility dysfunction due to decreased collagen levels and the formation of highly tyrosine-crosslinked collagen, potentially reducing their flexibility. In GMC101 mutant worms, vitamin B12 deficiency-induced oxidative stress triggers dityrosine-crosslinked amyloid β formation, which might promote its stabilization and toxic oligomerization.

Protein Nanofibrils and Their Hydrogel Formation with Metal Ions

Protein nanofibrils (PNFs) have been prepared by whey protein fibrillation at low pH and in the presence of different metal ions. The effect of the metal ions was systematically studied both in terms of PNF suspension gelation behavior and fibrillation kinetics. A high valence state and a small ionic radius (e.g., Sn4+) of the metal ion resulted in the formation of hydrogels already at a metal ion concentration of 30 mM, whereas an intermediate valence state and larger ionic radius (Co2+, Ni2+, Al3+) resulted in the hydrogel formation occurring at 60 mM. A concentration of 120 mM of Na+ was needed to form a PNF hydrogel, while lower concentrations showed liquid behaviors similar to the reference PNF solution where no metal ions had been introduced. The hydrogel mechanics were investigated at steady-state conditions after 24 h of incubation/gelation, revealing that more acidic (smaller and more charged) metal ions induced ca. 2 orders of magnitude higher storage modulus as compared to the less acidic metal ions (with smaller charge and larger radius) for the same concentration of metal ions. The viscoelastic nature of the hydrogels was attributed to the ability of the metal ions to coordinate water molecules in the vicinity of the PNFs. The presence of metal ions in the solutions during the growth of the PNFs typically resulted in curved fibrils, whereas an upper limit of the concentration existed when oxides/hydroxides were formed, and the hydrogels lost their gel properties due to phase separation. Thioflavin T (ThT) fluorescence was used to determine the rate of the fibrillation to form 50% of the total PNFs (t1/2), which decreased from 2.3 to ca. 0.5 h depending on the specific metal ions added.

Studies on the synthesis and stability of α-ketoacyl peptides

Oxidative stress, an excess of reactive oxygen species (ROS), may lead to oxidative post-translational modifications of proteins resulting in the cleavage of the peptide backbone, known as α-amidation, and formation of fragments such as peptide amides and α-ketoacyl peptides (α-KaP). In this study, we first compared different approaches for the synthesis of different model α-KaP and then investigated their stability compared to the corresponding unmodified peptides. The stability of peptides was studied at room temperature or at temperatures relevant for food processing (100 °C for cooking and 150 °C as a simulation of roasting) in water, in 1% (m/v) acetic acid or as the dry substance (to simulate the thermal treatment of dehydration processes) by HPLC analysis. Oxidation of peptides by 2,5-di-tert-butyl-1,4-benzoquinone (DTBBQ) proved to be the most suited method for synthesis of α-KaPs. The acyl side chain of the carbonyl-terminal α-keto acid has a crucial impact on the stability of α-KaPs. This carbonyl group has a catalytic effect on the hydrolysis of the neighboring peptide bond, leading to the release of α-keto acids. Unmodified peptides were significantly more stable than the corresponding α-KaPs. The possibility of further degradation reactions was shown by the formation of Schiff bases from glyoxylic or pyruvic acids with glycine and proven through detection of transamination products and Strecker aldehydes of α-keto acids by HPLC–MS/MS. We propose here a mechanism for the decomposition of α-ketoacyl peptides.

Enhanced functionality of pea-rice protein isolate blends through direct steam injection processing

Direct steam injection (DSI) processing with pH adjustment was investigated to enhance the functionality of pea-rice protein isolate blends (PR). Protein slurries at concentration of 5%(w/w) of commercial pea and rice protein isolates in the ratio of 2:1(w/w) across a range of steam temperatures (66-107°C) and pH values (2-11) were studied. After DSI treatment, the PR were freeze-dried to obtain the final dry protein powder. Based on protein solubility profiles, the optimal DSI processing conditions were 107°C and pH 11. Available lysine was not reduced (P>0.05) in the blend. Solubility (from 3 to 41%, at pH 7), emulsifying activity index (from 5.9 to 52.5m2/g), foam stability (from 68.2 to 82.8%), and oil holding capacity (from 1.8 to 4.9g/g) values increased (P<0.05) compared to the untreated PR. DSI can modify the functionality of PR without affecting the essential amino acid composition.

Nutritional profile of phytococktail from trans-Himalayan plants

We estimated the nutritive value, vitamin content, amino acid composition, fatty acid content, and mineral profile of a phytococktail comprising sea buckthorn (Hippophae rhamnoides), apricot (Prunus armeniaca), and roseroot (Rhodiola imbricata) from trans-Himalaya. The free vitamin forms in the phytococktail were determined by rapid resolution liquid chromatography/tandem mass spectrometry (RRLC-MS/MS). Vitamin E and B-complex vitamins were detected as the principle vitamins. Reversed-phase high performance liquid chromatography (RP-HPLC) with pre-column derivatization was used for identification and quantification of amino acids. Eight essential and eleven non-essential amino acids were quantified, and the content ranged between 76.33 and 9485.67 µg/g. Among the essential amino acids, L-methionine, L-phenylalanine, L-lysine, L-leucine, and L-histidine were found to be the dominant contributors. We also quantified the fatty acids in the phytococktail by using gas chromatography coupled with a flame ionization detector (GC-FID) with fatty acid methyl esters (FAMEs) derivatization. The analysis revealed the presence of 4 major fatty acids contributing to the total lipid content. Palmitic acid was found to be the rich source of saturated fatty acid (SFA) and constituted ∼31% of the total lipid content. Among the unsaturated fatty acids (UFAs), palmitoleic acid (43.47%), oleic acid (20.89%), and linoleic acid (4.31%) were prominent. The mineral profiling was carried out by inductively coupled plasma optical emission spectrometer (ICP-OES), and it was found to contain a number of important dietary mineral elements. The harsh climatic conditions, difficult terrain, and logistic constraints at high altitude regions of Indian trans-Himalayan cold desert lead to the scarcity of fresh fruits and vegetables. Therefore, the source of multiple vitamins, essential amino acids, fatty acids, and dietary minerals from the phytococktail would provide great health benefit in the stressful environment and could be used as a high value nutritional supplement.

Contribution of sulfur-containing compounds to the colour-inhibiting effect and improved antioxidant activity of Maillard reaction products of soybean protein hydrolysates

BACKGROUND

Light-coloured and savoury-tasting flavour enhancers are attractive to both consumers and food producers. The aim of this study was to investigate the colour-inhibiting effect of L-cysteine and thiamine during the Maillard reaction of soybean peptide and D-xylose. The correlation between volatile compounds and antioxidant activity of the corresponding products was also studied.

RESULTS

Colour formation was markedly suppressed by cysteine. Compared with peptide/xylose (PX), the taste profile of Maillard reaction products (MRPs) derived from peptide/xylose/cysteine (PXC) and peptide/xylose/cysteine/thiamine (PXCT) was stronger, including umami, mouthfulness, continuity, meaty and overall acceptance. PXC and PXCT also exihibited distinctly higher antioxidant activity. Principal component analysis was applied to investigate the correlation between antioxidant activity and volatile compounds. Of 88 volatile compounds identified, 55 were significantly correlated with antioxidant activity by two principal components (accounting for 85.05% of the total variance).

CONCLUSION

Effective colour control of the Maillard reaction by L-cysteine may allow the production of healthier (higher antioxidant activity) and tastier foods to satisfy consumers' and food producers' demands. Light-coloured products might be used as functional flavour enhancers in various food systems.

Temporal regulation of cuticle synthesis during development of Caenorhabditis elegans

The pattern of cuticle protein synthesis during development of the nematode Caenorhabditis elegans has been studied using NaH14CO3. Both pulse-labeling and pulse-chase-labeling experiments indicate that synthesis of cuticle components occurs at high levels during the molting periods and at much reduced rates during the intermolt periods. No such discontinuous pattern is observed for the synthesis of total noncuticle macromolecules during development. The soluble and insoluble proteins of the cuticle, which comprise the inner and outer cuticle layers, respectively, follow similar patterns of synthesis during the two molts examined. At each molt the structural components of the cuticle account for approximately 10% of the total macromolecules labeled by NaH14CO3. No evidence is found for reuse of cuticle material between successive developmental stages of C. elegans.

Change in amino acid composition of different protein sources after rumen incubation

The effective degradability (Dg) of dry matter (DM), nitrogen (N) and amino acids (AA) in soya-bean meal (SBM), fish meal (FM), dried brewers' grains (DBG) and ensiled lucerne (EL) was measured using polyester bags suspended in the rumens of six cows given a basal diet of maize silage, hay and concentrate. Rumen outflow rate was measured using chromium-mordanted SBM.

AA were grouped into essential (EAA), non-essential (NEAA) or branched chain (BrAA). The AA concentration in DM varied from 88 g/kg DM for EL to 566 g/kg for FM. The proportion of determined AA in crude protein (CP) was similar for SBM, FM and DBG and always higher than 0·85. EL had the lowest A A concentration in CP, partly due to the presence of ammonia N (170 g/kg total N).

Methionine always had a higher, and threonine a lower Dg than total AA in all foods. Dg of other AA was generally food dependent.

SBM always had the highest EAA, BrAA, NEAA, mean AA and total N degradability, whilst FM always had the lowest Dg for EAA, BrAA, mean AA and total N, and these values were significantly different in comparison with SBM. The effective Dg of BrAA in DBG was significantly lower than in SBM and significantly higher than in FM. In EL, NEAA and mean AA Dg were significantly lower compared with SBM.

Effective Dg of total AA in SBM and EL was significantly lower than the CP Dg; this difference was not apparent in DBG or FM.

The undegraded fraction of FM and EL had a significantly higher proportion of EAA whilst DBG and EL had a higher proportion of BrAA when compared with the unexposed food. Isoleucine concentration, highest in EL, and lysine and methionine contents, highest in FM, differed significantly between the four protein source residues.

The first limiting AA after rumen incubation, in relation to casein and meat, was always methionine. The essential amino acid index of the food residues post incubation, relative to casein and meat, was lower in SBM, DBG and EL but higher in FM.

Synthesis and release of dopamine in rat striatal slices: requirement for exogenous tyrosine in the medium

When incubated in a tyrosine-free medium, the tissue dopamine (DA) level of rat striatal slices increased by about 921 +/- 15 pmol/mg protein during 90 min of preincubation. In contrast, the tissue-free tyrosine level declined only 130 pmol/mg protein in the same assay period. Depolarization of the slices with high K+ increased both DA and DOPAC outputs and depleted tissue DA level by about 75%. Although 60 min of resting after high K+ depolarization significantly restored the tissue DA levels, neither this restoration nor depolarization-induced DA release was altered by exogenous tyrosine. Similarly, failure of exogenous tyrosine was also observed during three successive depolarization periods of striatal slices. These results indicate that nigrostriatal dopaminergic neurons are able to synthesize and release the DA in the absence of exogenous tyrosine in the medium. Since the free tyrosine level in the slices does not seem to be a sufficient source, it is likely that tyrosine mobilized from its bound source(s) supports the DA synthesis under in vitro experimental conditions.

Characterization of epitope regions of thyrotropin beta-subunit recognized by the monoclonal antibodies mAb279 and mAb299: a chimeric peptide approach

This investigation describes the design, synthesis and evaluation of chimeric peptides related to the bovine thyrotropin beta-subunit, bTSHbeta. The structures of these chimeric peptides were derived from investigations with linear peptides and sequence alignment studies, in association with a homology model of TSHbeta developed from the hCG X-ray crystallographic structure. The structures of these chimeric peptides comprised beta-turn regions of loop L1 [bTSHbeta(14-20)] and loop L3 [bTSHbeta(65-72)] held in close proximity by a bis-beta-alanine linker and the disulfide bond bTSHbeta[Cys16-Cys67]. Linear and cyclic chimeric peptides were evaluated in immunochemical assays for their ability to inhibit the binding of radio-iodinated bTSHbeta [125I-bTSHbeta] to the monoclonal antibodies, mAb279 and mAb299. Previously, mAb279 and mAb299 have been shown to recognize epitopes accessible on the surface of TSHbeta that lie in close proximity to the TSH receptor-binding site. The results indicate that these chimeric peptides can specifically inhibit in a dose-dependent manner the binding of 125I-bTSHbeta to mAb299, while having a lesser effect on the binding with mAb279. Based on these results, it can be concluded that the bTSHbeta-epitope recognized by mAb299 involves contributions from amino residues from the beta-turn regions of the L1 and L3 loops of TSHbeta, and that these loop regions flank part of the receptor binding site of the bTSH beta-subunit.

Hydrolysis and amino acid composition of proteins

Amino acid composition analysis is a classical protein analysis method, which finds a wide application in medical and food science research and is indispensable for protein quantification. It is a complex technique, comprising two steps, hydrolysis of the substrate and chromatographic separation and detection of the residues. A properly performed hydrolysis is a prerequisite of a successful analysis. The most significant developments of the technology in the last decade consist in the (i) reduction of the hydrolysis time by the use of microwave radiation energy; (ii) improvement in the sensitivity of the residue detection, the quantification of the sensitive residues and separation of the enantiomeric forms of the amino acids; (iii) application of amino acid analysis in the large-scale protein identification by database search; and (iv) gradual replacement of the original ion exchange residue separation by reversed-phase high-performance liquid chromatography. Amino acid analysis is currently facing an enormous competition in the determination of the identity of proteins and amino acid homologs by the essentially faster mass spectrometry techniques. The amino acid analysis technology needs further simplification and automation of the hydrolysis, chromatography and detection steps to withstand the pressure exerted by the other technologies.

Comparison of serine and hippurate as precursor equivalents during infusion of [15N]glycine for measurement of fractional synthetic rates of apolipoprotein B of very-low-density lipoprotein

Enrichment in hippurate has been measured to indicate precursor enrichment during glycine tracer infusion studies to estimate fractional synthetic rates of individual hepatic export proteins. However, hippurate tends to overestimate precursor enrichment. Since glycine is rapidly converted to serine by liver cells, we compared tracer enrichment in hippurate and serine with that of glycine incorporated into apolipoprotein (apo) B-100. Ten healthy control subjects were studied in the postabsorptive state during an 8-hour primed-constant infusion of [15N]glycine (10 mumol.kg-1.h-1). Apo B of very-low-density lipoprotein (VLDL) was isolated by standard ultracentrifugation and isopropanol precipitation. Glycine and serine were isolated from plasma and hydrolyzed apo B, hippurate was isolated from plasma, and [15N]enrichment was determined by gas chromatography-mass spectrometry. Enrichment in serine and glycine isolated from apo B was identical at all time points, and their enrichment in apo B increased asymptotically, approaching an apparent plateau (mean +/- SD: 91% +/- 10% of calculated plateau at 8 hours) that was taken to represent hepatic protein precursor enrichment. Enrichment in both plasma serine and hippurate followed a biphasic pattern and continued to increase until the end of the study, raising the possibility that precursor enrichment had not reached a steady state during the study. The apo B plateau was lower (factor 0.76 +/- 0.27) than the final enrichment in hippurate and higher (factor 1.38 +/- 0.36) than that in plasma serine; however, predictions of protein precursor enrichment based on either metabolite were flawed by a large coefficient of variation (35% v 26%).(ABSTRACT TRUNCATED AT 250 WORDS)

A computer program to determine a protein sequence from an amino acid analysis

We have developed a computational method for analyzing the proteolytic products of a protein, knowing its sequence and the amino acid percentages of its products. For all fragments, amino acid percentages are calculated and compared to the experimental results (calculating the error within the experiment). The program keeps the best fitted fragment using a least squared method. This program was written to determine the sequence of the proteolytic products that appeared during the purification of annexin I domain 2. The reliability of the method was verified in this case. However the latter depends on the length and on the amino acid composition of the entire protein and of its fragments. This program may be suitable for analyzing the sequence of the products in any protease digestion, whether designed or accidental.

No evidence for feedback inhibition of hepatic apolipoprotein B (apo B) production after extracorporeal low density lipoprotein precipitation as determined by [1-13C]leucine infusion in normal volunteers

To determine the impact of an acute reduction of the circulating mass of apolipoprotein B (apo B) on apo B metabolism we studied six healthy male volunteers before (day 0), 1 day after (day 2), and 7 days after (day 8) an LDL apheresis treatment which reduced apo B mass by 59%. Appearance of newly synthesized apo B in plasma VLDL and LDL was studied using a primed-constant infusion of [1-13C]-leucine. VLDL apo B pool size and fractional VLDL apo B production rate calculated using a one-compartment model were similar on all 3 study days. Absolute VLDL apo B production was not statistically different throughout the study (19.7 +/- 12.3, 19.5 +/- 7.5, 29.1 +/- 17.7 mg kg-1 day-1). LDL apo B fractional production rate was increased on day 2 (0.38 +/- 0.17, 0.68 +/- 0.08, 0.37 +/- 0.06 pools day-1 on days 0, 2, and 8; P < 0.01). Absolute LDL apo B production, however, remained constant throughout the study (10.8 +/- 3.3, 11.0 +/- 1.9, 10.8 +/- 3.1 mg kg-1 day-1). We conclude that in healthy male volunteers acute reduction of the circulating apo B mass by LDL apheresis does not affect apo B metabolism significantly.

Determination of amino sugars in synthetic glycopeptides during the conditions of amino acid analysis utilizing precolumn derivatization and high-performance liquid chromatographic analysis

The growing number of synthetic glycopeptides required an in-house method for the analysis of the final products. A reversed-phase high-performance liquid chromatographic protocol was developed to verify the presence of N-acetylglucosamine and N-acetylgalactosamine in synthetic glycopeptides after hydrolysis and derivatization with 4-dimethylaminoazobenzene-4'-sulphonyl chloride. Different sugar and glycoamino acid standards were used to separate the two carbohydrate moieties, and the location of the derivatized 2-aminoglucose was established by the use of radiolabeled sugar. The utility of the approach is demonstrated by the amino acid analysis of N- and O-glycosylated synthetic peptides and the method could provide an alternative for sugar analysis of glycoproteins.

Analysis of plasma hippurate in humans using gas chromatography-mass spectrometry: concentration and incorporation of infused [15N]glycine

To allow in vivo determination of synthetic rates for individual proteins, physiological incorporation of infused [15N]glycine into urinary hippuric acid has been used as an indicator of intrahepatic tracer dilution. Although the kidneys might contribute to hippurate production, the relationship between hepatic, plasma, and urinary hippurate has not yet been established in humans. To further investigate these issues we developed a fast, sensitive, and reliable method for measuring simultaneously hippurate concentrations and in vivo tracer incorporation into hippurate in plasma and urine using stable isotopes and gas chromatography-mass spectrometry. We then tested this assay under several experimental conditions. Reference compounds [( 15N]- and [ring-2H5]hippurate) were synthesized and gave linear standard curves. Postabsorptive hippurate plasma levels in healthy subjects ranged from 1.2 to 10.5 microM and protein binding was 79 +/- 6% (mean +/- SD). Following a bolus dose of [15N]glycine tracer appeared in plasma hippurate; enrichment in hippurate was indistinguishable from that in glycine after an equilibration period of 20 min, indicating a close relationship between intracellular glycine and plasma hippurate. A 16-h infusion of [15N]glycine resulted in identical enrichment levels in urinary and plasma hippurate; glycine enrichment in a hepatic export protein (VLDL-ApoB) was approaching plasma hippurate but not plasma free glycine enrichment. The ability to monitor plasma hippurate is of practical advantage compared to the sampling of urine. Furthermore it allows the monitoring of rapid events in the intrahepatic dilution of an infused glycine tracer. This assay may, therefore, become an important tool in the study of hepatic protein metabolism.

[Incorporation of 15N in VLDL and LDL: in vivo synthesis of apolipoprotein B in the post-absorptive and fasting state]

In vivo synthesis of apolipoprotein B 100 (ApoB) was recently determined in man using stable isotopes. With this procedure we analyzed (1) the effect of fasting on synthesis of ApoB from very low density lipoprotein (VLDL) and (2) tracer enrichment in low density lipoprotein (LDL). After a 36-hour fasting period and in the post-absorptive state 4 healthy subjects were given a priming dose (8.7 mumol/kg) of 15N glycine followed by a constant infusion (10 mumol/kg/h for 8 h) to achieve 5% tracer enrichment in the plasma pool of glycine. The K-values, i.e. fractional synthetic rates/hr of ApoB from VLDL were 0.53 +/- 0.26 vs. 0.43 +/- 0.16 (p greater than 0.05). Tracer enrichment in ApoB from LDL at the end of the infusions was 0.19% vs. 1.46% in ApoB from VLDL. The results indicate that (1) in young healthy postabsorptive individuals about 40% of ApoB from VLDL in plasma is synthesized per hour, (2) fasting does not materially affect fractional ApoB synthesis and (3) at 5% 15N enrichment in plasma glycine, tracer enrichment in ApoB from LDL is at the lower limit of detection for the procedure employed.

Amino acid analysis utilizing phenylisothiocyanate derivatives

Advances in liquid chromatography have brought about the development of new techniques in amino acid analysis which take full advantage of precolumn derivatization procedures. Using phenylisothiocyanate as the reagent, detection limits under 1 pmol can be routinely achieved, allowing the analysis of submicrogram protein samples. Analysis times as short as 10 min for samples after hydrolysis and 1 h for physiologic samples are possible. Accurate, reproducible quantitation of amino acids can be obtained from complex matrices such as plasma, urine, feed, and food samples. This level of performance and flexibility gives the analyst the first realistic alternative to ion-exchange analysis without compromising desirable features of the traditional methodology.

Isolation and structure analysis of bee venom mast cell degranulating peptide

The venom of Apis mellifera was processed by gel permeation chromatography on Sephadex G-50 and by reversed-phase HPLC. The initial gel permeation step was carried out in the presence of phosphate ions (0.5 M). Ion pair reagents were required to resolve the strongly basic peptides, secapin, mast cell degranulating (MCD-) peptide and apamin, by reversed-phase (RP) HPLC. Using this relatively simple procedure it is possible to isolate these peptides essentially free of melittin (less than 1 in 10(7)) and phospholipase (less than 1 in 10(5] in high yield. The CD spectrum and secondary structure analysis are reported for MCD-peptide and on this basis a solution structure is proposed for this toxin.

Activation of nonspecific lipase (EC 3.1.1.-) by bile salts

The enzyme nonspecific lipase (EC 3.1.1.-) from rat pancreas has been isolated and its amino acid composition determined. The amino acid composition confirms more indirect evidence that nonspecific lipase is not the same enzyme as cholesteryl ester hydrolase. Activation of the enzymatic activity by bile salts has been studied by equilibrium dialysis, gel filtration, light scattering, circular dichroism and fluorescence polarization. The binding of bile salt by the enzyme is saturable and is associated with a conformational change. Upon binding cholate, the protein experiences a decrease in beta-structure with no significant change in alpha-helix content, an increase in apparent Stokes radius, a decrease in light scattering properties, and a slight decrease in polarization of the intrinsic tryptophan fluorescence. Attachment of bile salt is associated with decreased reactivity of essential sulfhydryl groups, but no detectable change in reactivity of amino groups. A change to a more nearly spherical shape upon binding bile salt would be consistent with the experimental observations, but the exact sites of binding remain uncertain.

Amino acid analysis of bone from a possible case of prehistoric iron deficiency anemia from the American southwest

It is possible that dietary conditions can result in the production of abnormal bone protein. For example, a heavily maize-dependent diet could be deficient in one or more essential amino acids necessary to normal human biochemistry and consequently necessary for normal bone protein synthesis. Amino acid analysis of bone tissues, thus, could provide a useful diagnostic tool in paleopathology. To test this potential we have compared the amino acid analyses of bone samples from a prehistoric Southwest Indian child exhibiting porotic hyperostosis with samples taken from (1) two children's skeletons lacking bone lesions but from the same area and time, (2) a modern child who died from accidental causes, and (3) adult human compact bone. Analytical results of the nonpathological prehistoric specimens were virtually identical to that of the modern infant, indicating remarkable preservation of bone protein. The pathological bone sample differed from the three control specimens by having as much as 25% less of those amino acids containing hydroxyl group and acidic side chains. We interpret the amino acid profile for the diseased child as indicating the presence of a greater proportion of helical protein (or less noncollagenous protein) as well as a lowered degree of hydroxylation of proline and lysine. One explanation for our data is that protein biosynthesis is altered in the child exhibiting porotic hyperostosis, and either some proteins important in the early phases of mineralization are not produced in sufficient quantity, or some necessary enzyme cofactors (e.g., dietary ferrous ions) are missing. We conclude that our data are compatible with, but do not prove, the hypothesis that the porotic hyperostosis exhibited by the Southwest Indian child is the result of iron deficiency anemia.

Isolation and characterization of adult bovine heart muscle chalones

A three-step purification procedure for the isolation of heart muscle chalones is described. The method uses ultrafiltration followed by concanavalin A-Sepharose affinity chromatography and subsequent sucrose density gradient centrifugation. Analytical ultracentrifugation of the highly purified chalone fraction indicated a sedimentation coefficient of 16.7 S and an average Mr of 715,527. Chemical analyses have confirmed this protein to be a glycoprotein, and polypeptide analysis indicated the involvement of identical subunits in its composition. In vivo studies confirmed that the chalone isolated from adult bovine hearts inhibits DNA synthesis of newborn hamster hearts. In addition, it was found to be tissue and not species specific and had no cytotoxic effects on the target cells.

Human milk ribonuclease

Two components having ribonuclease (EC 3.1.27.5) activity were isolated from human milk. Each component of human milk ribonuclease (RNAase) moved at a slightly different rate when electrophoresed on polyacrylamide gel but at the same rate when ultracentrifuged. The major component had a molecular weight of approx. 14 000, an isoelectric point of pH 7.9, and exhibited a broad absorbance maximum between 277 and 281 nm. Human milk RNAase hydrolyzed yeast RNA, poly(cytidylic acid) and poly(uridylic acid) but not DNA, poly(adenylic acid) or poly(guanylic acid). Maximum activity occurred at pH 7.7 and 60 degrees C. Amino acid analysis of the major component revealed a large number of alanine, valine, glycine and aspartic acids but no tryptophan or free sulfhydryl groups. Lysine was the N-terminal amino acid. Tryptic hydrolysis yielded 18 peptides, some of which are similar to those from bovine pancreatic RNAase. Human milk RNAase activity was increased in the presence of NaCl, KCl and sodium citrate and decreased by CaCl(2), MgCl(2), FeSO(4), ZnSO(4) and CuSO(4).