COLLAGEN METABOLISM IN THE NORMAL AND LATHYRITIC CHICK

1. Radioisotope incorporation studies of normal and lathyritic chick embryo bone collagen do not demonstrate any interference by lathyrism with collagen synthesis or fibril formation. 2. The results indicate that a portion of the extractable collagen from lathyritic chick embryo bone represents newly synthesized protein. Evidence from a double labeling experiment and from analysis of isotope flow between the extractable and non-extractable pools suggests the extractable lathyritic collagen is heterogeneous. We propose that the lathyritic process affects collagen in all states of aggregation, probably in varying degree. 3. Puromycin, administered intravenously, reduces the amount of extractable collagen in both normal and lathyritic chick embryo bone, and diminishes the incorporation of labeled proline into collagen. 4. Marked fluctuations in incorporation of labeled amino acids into chick embryo bone collagen suggests the occurrence of wide fluctuations in metabolism of this protein.

THE PERIODATE OXIDATION OF AMINO ACIDS WITH REFERENCE TO STUDIES ON GLYCOPROTEINS

1. All alpha-amino acids are oxidized by periodate, but at different rates. 2. The rates of oxidation of individual alpha-amino acids vary with pH. In general, oxidation proceeds more rapidly at alkaline pH. 3. Serine, threonine, cysteine, cystine, methionine, proline, hydroxyproline, tryptophan, tyrosine and histidine are rapidly and extensively oxidized by periodate. 4. Cysteine, cystine, methionine, tryptophan, tyrosine and histidine are oxidized by periodate when they are substituted in the carboxyl and amino groups, as in a polypeptide chain.

GLYCYL-PROLINE IN URINE OF HUMANS WITH BONE DISEASE

An unknown ninhydrin-reacting substance has been found in the urine of three human subjects with rickets. A sample of the substance separated from urine by elution chromatography was hydrolyzed in acid, and equimolar amounts of glycine and proline were released. The DNP reaction applied to the substance resulted in DNP-glycine and free proline. The isolated unknown substance and glycyl-L-proline cochromatographed and coelectrophoresed in a number of solvent and buffer systems. The substance was therefore identified as glycyl-proline.Glycyl-proline is apparently excreted from plasma into urine; it is poorly absorbed by the kidney and its transport is independent of either the glycine or the L-proline transport mechanisms.Glycyl-proline was not excreted by normal subjects. It was found only in patients with severe active rickets. Glycyl-proline excretion paralleled that of total bound hydroxyproline, both diminishing as the rickets healed. Bone collagen appears to be the likely source for glycyl-proline in these patients.

METABOLISM OF COLLAGEN IN MAMMALIAN TISSUES

The amino acid composition of collagen is described and the status of knowledge about the synthesis of its unique amino acids, hydroxyproline and hydroxylysine, presented. This is followed by a schematic overview of collagen metabolism. Scurvy and lathyrism, the only two abnormalities of collagen metabolism which can now be reasonably elucidated at a molecular level, are then discussed in some detail. The paper concludes by stressing the importance of recognizing the role of histoarchitecture and of interactions of collagen with other compounds when studying collagen or its metabolism in the whole animal.

AN IMPROVED COLORIMETRIC METHOD FOR THE DETERMINATION OF PROLINE IN THE PRESENCE OF OTHER NINHYDRIN-POSITIVE COMPOUNDS

1. The conditions required for sensitive and specific colorimetric determination of proline with acidified ninhydrin were investigated. 2. A method applicable to protein samples was developed. 3. The only compound found to interfere appreciably was a hydroxyproline.

RAT MAMMARY GLAND METABOLISM RELATIVE TO EPITHELIAL AND CONNECTIVE TISSUE CONTENT

The respiration rate of rat mammary gland slices increased directly with the epithelial proliferation induced by pregnancy and lactation. In the absence of glucose the respiration was depressed, particularly in slices with the largest epithelial content. Dinitrophenol (5 x 10–5 m) provided a metabolic distinction between the epithelium of pregnant and lactating mammary glands; it stimulated the respiration of the former and depressed the respiration of the latter. The rate of anaerobic glycolysis (q1acN2) for mammary epithelium was adduced to be 4–5 µl/hr mg dry nonfat tissue and the rate remained in that range during lactation and pregnancy; the rate of aerobic glycolysis increased during pregnancy and decreased during lactation. Alkaline phosphatase activity did not vary directly with the mammary epithelium content and it was suggested that the rate of epithelial cell proliferation (mitoses) and hormonal factors might also be of importance in determining the total activity observed. The increase in glucose 6-phosphate dehydrogenase and 6-phosphogluconic acid dehydrogenase activity during pregnancy and at the onset of lactation was not directly related to the increase in mammary epithelium.

EFFECTS OF SHORT TERM ADMINISTRATION OF PHYSIOLOGICAL DOSES OF HUMAN GROWTH HORMONE IN THREE PATIENTS WITH TURNER'S SYNDROME

The effect of apparently physiological doses of human growth hormone was investigated in three patients with Turner's syndrome in short term metabolic balance studies. The subjects presented an abnormal sex chromosome constitution and an increased level of sulphation factor activity in serum.

Two dose levels of hormone were used, and there appeared an anabolic response to both. No correlation with dose was obtained for any of the parameters used except for urinary magnesium, where the retention was greater with the higher dose. The sulphation factor activity of serum increased during hormone administration in the one case studied in this respect.

The urinary excretion of hydroxyproline was within the normal range in the two patients studied in this respect, and was not altered by growth hormone.

All patients had an increased urinary excretion of creatine which at present cannot be explained. The creatinuria diminished during growth hormone treatment.

The mechanism behind the retarded growth is discussed. It is suggested that a major factor might be a defect in the center for linear growth, i. e. the epiphyses that would make these less responsive to all the factors normally stimulating the growth processes in the epiphyseal zones.