Collagen and its rational content in meat products: Part 1. Analytical studies.

Computer-assisted simulation has been used to study the effect of collagen content on the biological value of meat proteins. It has been shown that an increase in the collagen content from 2·5% to 15-20% of the total amount of proteins contained in minced meat tangibly enhances protein utilization for tissue synthesis. Hence, the above collagen content in meat products heightens their nutritional and biological value and renders them more suited for human metabolism.

Collagen and its rational content in meat products 2: Experiments with growing rats.

Experiments with growing rats have been carried out to determine the specific changes in the biological value of finely minced meat following an increase in the total ratio of collagen from 6·1% to 21·2% of the total proteins. It has been established that within the above range the biological value and net protein utilization tended to drop, the difference being statistically insignificant. At the same time, an increase in the collagen content to 14·5% did not reduce the efficiency of tissue protein biosynthesis. It has been demonstrated that the above differences in the biological value for humans and rats are due to their varied requirements for protein composition. Therefore, the results obtained do not contradict the conclusion favouring a positive effect of a 15-20% increase in the total ratio of collagen on the efficiency of utilizing meat proteins for the human body's biosynthesis.

Iron absorption from meat and meat products: Part I-Theoretical foundations for estimating available iron.

A theoretical foundation is developed to estimate available meat iron. Iron absorption factors are calculated for various kinds of raw meat. A methodology for estimating available iron from finished meat products, depending on the content of different meat ingredients, is suggested.

Iron absorption from meat and meat products: Part 2-Iron absorption from high-roughage meat products.

The main reasons for the inhibiting effect of dietary fibre on meat iron absorption in the intestine are examined. A model experiment estimates binding of iron by the dietary fibre (DF) of wheat bran. A radioactive tracer method was applied to volunteers to detect the availability of iron from fibrous meat foods. The evidence suggests that incorporating up to 2% of dietary fibre into meat products reduces iron absorption factors by no more than 1-2%. Adding ascorbic acid in the presence of DF lowers them only by 0·1-0·5%, i.e. it does not damage iron absorption processes.

Comparison of some properties of chromatin non-histone proteins and nuclear sap proteins.

The properties of rat liver and thymus non-histone and nuclear sap proteins were compared. The distribution of total, labile-bound and 0.35 M NaCl extractable non-histone proteins from one organ on polyacrylamide-gel electrophoresis in the presence of sodium dodecylsulphate is quite similar. On electrophoresis non-labelled and 32P-labelled non-histone and nuclear sap proteins from one organ differ from one another both qualitatively and quantitatively. We did not find an appreciable difference between non-labelled non-histone proteins isolated from liver and thymus. The distribution of 32P-labelled non-histone proteins from various organs differs quantitatively rather than qualitatively. Non-labelled and 32P-labelled nuclear sap proteins from liver and thymus differ significantly. 'Free' nuclear sap proteins and the proteins of ribonucleoprotein particles from thymus nuclei contain a great quantity of identical polypeptides, whereas other polypeptides are specific to each of these protein fractions. Upon incubation of nuclei with [gamma-32P]ATP the label is incorporated into all the fractions of nuclear protein. The nuclear proteins are phosphorylated at decreasing rates in the order: labile-bound non-histone proteins greater than firmly bound non-histone proteins greater than 'free' nuclear sap proteins = proteins of ribonucleoprotein particles greater than histones. Nuclear sap and non-histone proteins contain protein kinases capable of phosphorylating both these proteins and histones. Histone phosphorylation is sharply inhibited after addition of DNA, the protein kinases of nuclear sap phosphorylating less effectively the histones complexed with DNA than the non-histone proteins. Both non-histone and nuclear sap proteins contain fractions interacting in vitro with DNA. Denatured DNA binds twice as much 32P-labelled nuclear sap proteins and a little more 32P-labelled non-histone proteins than native DNA. Denatured DNA binds non-histone and nuclear sap proteins much more effectively than native DNA. It was shown by the membrane filter technique that the major part of the nuclear sap and non-histone proteins interacting with native DNA binds to it non-specifically. A certain portion of non-histone and nuclear sap proteins interacts specifically with homologous denatured DNA. The possible role of non-histone and nuclear sap proteins in the regulation of transcription is discussed.

Specific interaction of chromatin non-histone proteins with DNA.

The interaction of different preparations of chromatin non-histone proteins of rat liver and thymus with homologous and heterologous DNA was studied. It is shown by the method of fixation of non-histone proteins-DNA complexes on nitrocellulose filters that: (1) all the non-histone proteins preparations studied form complexes with DNA in 0.02 M Tris--HCl (pH 7.5)--3 mM MgCl2; (2) the main part of non-histone proteins interacting with DNA binds to it non-specifically; (3) a small part of non-histone proteins interacts specifically with the homologous native DNA in 5 M urea; (4) both homologous and heterologous denatured DNA binds non-histone proteins more effectively than the native one; (5) the specific interaction of non-histone proteins with the homologous denatured DNA is observed both without urea and in its presence. The specific interaction of a small part of non-histone proteins with the homologous native and denatured DNA is also shown by the method of non-histone proteins chromatography on polyacrylamide--agarose columns containing DNA. The data obtained are discussed in the light of the possible non-histone proteins role in the specific regulation of the transcription process.