The solid-phase chemical synthesis of ubiquitin produced a molecule with physicochemical properties similar to those of the natural protein. We have grown crystals of this synthetic ubiquitin and performed an X-ray analysis at 1.8 A resolution in order to compare the synthetic protein with the known natural structure. The crystals were isomorphous with those of the natural protein, the R-factor between them being 7.1%. Difference Fourier analysis shows that the synthetic and natural structures are indistinguishable. The co-ordinates of the natural ubiquitin (1UBQ) were used as the starting point for restrained least-squares refinement (TNT program) against the synthetic X-ray data. The refinement converged to R = 16.5% and the resulting model did not change when refined against natural ubiquitin X-ray data (R = 18.7%). From both the refinement and featureless difference Fourier synthesis, we conclude that the synthetic and natural protein structures are identical. A short discussion about the uses of proteins with 'non-standard' amino acid residues is included.

Analytical results are given for whey powders prepared on a commercial or semi-commercial scale by three companies. Altogether, five preparations enriched in ␤-lactoglobulin, four whey protein isolates and a fraction enriched in ␣-lactalbumin were analyzed for protein composition, including % ␤-lactoglobulin, ␣-lactalbumin, bovine serum albumin, casein (glyco) macropeptide and the main triglycerides. Protein composition was determined by high pressure gel permeation and reversed phase liquid chromatography and by capillary zone electrophoresis. The extent of modification of the native ␤-lactoglobulin structure was also measured through the degree of lactosylation and the fraction of accessible free sulphydryl groups. One significant finding was that the calculated recovery of protein following quantitation of the chromatogram or electropherogram was seldom above 90% and occasionally below 60% of that loaded onto the column or capillary, raising doubts as to the reliability of the analytical results. Extrapolation by linear regression to 100% recovery allowed estimates to be made of the true ␤-lactoglobulin composition of the samples. The nine samples could be placed into three distinct groups with estimat-ed true ␤-lactoglobulin weight % of 70.9 Ϯ 1.1, 62.0 Ϯ 3.4 and 39.5 Ϯ 4.9. Physico-chemical properties of the group of samples are reported elsewhere (Holt et al., 1999).The inter-laboratory comparisons involved the Royal Veterinary and Agricultural University (KVL), two laboratories of BDI (Lab1 and Lab2), NIZO food research (NIZO) and the Composition of whey protein isolates and fractions C. Holt et al. Figure 2 RP-HPLC analysis of commercial whey protein samples using the LRTL method. A. MDFwpi-1, B. MDFwpi-1a, C. MDFwpi-1b.Figure 3 Capillary zone electropherograms of selected samples as obtained by the KVL method. Within the b-Lg region, lactosylated forms have longer migration times than the native forms. on the Molecular Basis of the Aggregation, Denaturation, Gelation and Surface Activity of Whey Proteins (MADGELAS), CT96-1202. All other members of the MADGELAS group are thanked for their co-operation in the sample survey, of which this paper forms a part. The HRI work was supported by the Scottish Office Composition of whey protein isolates and fractions C. Holt et al.

Insider report: A fluoroleucine mutant of ubiquitin (cyan) with two strategically placed fluorine reporter groups in its core was synthesised. 1H NMR, crystallography, CD spectroscopy, biological assay and calorimetry indicate minimal structural and functional perturbation compared to the native protein (yellow; see picture). 19F NMR spectra indicate changes within the core during folding and unfolding.

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The physico-chemical properties are reported for a group of whey protein powders prepared on a commercial or semi-commercial scale by three companies and chemically characterized as described elsewhere . The dependence of the apparent ␤-lactoglobulin % on the recovered % showed that the nine samples could be placed in three distinct groups with ␤-lactoglobulin weight % of 70.9 Ϯ 1.1 (Group 1), 62.0 Ϯ 3.4 (Group 2) and 39.5 Ϯ 4.9 (Group 3). Measurements by 1 H-NMR spectroscopy, on 3 of the samples confirmed that the native fold still predominated in the ␤-lactoglobulin. ␤-lactoglobulin could be crystallized from all the powders and the normal space group and cell dimensions were determined for the 8 samples that gave crystals of good enough quality for X-ray studies. Differential scanning microcalorimetry of samples dispersed in a phosphate buffer showed a clear difference between Goups 1 and 2 with a more prominent peak due to ␣-lactalbumin in the Group 2 samples. Light scattering and size exclusion chromatography showed that two types of aggregates were present to a variable extent in all the samples and after a heat treatment, the larger aggregates tended to predominate in