Enzymes of glycogen metabolism in chick embryo liver]

At all stages of ontogenesis glycogen phosphorylase (EC 2.4.1.1) from liver chick embryos in represented by an isoenzyme whose properties are close to those of isoenzyme IL or F. Total enzyme activity (a+b forms) from the 8th day of development up to hatching gradually increases 1.5-fold, a practically complete activation of enzyme being observed by the end of embryogenesis. Phosphorylase b possesses high catalytic activity in the presence of 1 mM AMP and it activated by protamine and 0.2 M Na2SO4. Glycogen synthetase (EC 2.4.1.11) has a constant Km(UDFG) value during ontogenesis. This value is about 5.10(-4) M in the presence of 10 mM glucose-6-phosphate, both for I- and D-forms of enzyme. The total enzyme activity reaches its maximum on the 17th postembryonic day and is decreased more than 6-fold thereafter. In the course of embryogenesis the I/D ratio is increased from 0.2 on the 8th day of development up to 0,45 during extensive accumulation of glycogen and falls down to 0.33 before hatching. Glycogen biosynthesis in embryonic liver is wellcorrelated with the increase in the I/D ratio, i.e. the increase of the active form of enzyme. The proportion of granular glycogen in embryonic liver is increased from 15% up to 90% of total glycogen content between the 8th and 14th days of development. The activity of glycogen synthetase contained in granular glycogen is increased from 40% in the 8-day-old embryos up to 90% in the 18-day-old ones. The activity of phosphorylase is found in granular glycogen only on the 12th day of embryogenesis and reaches its maximum (80% of total enzyme activity) only on the 19th days of development. It is concluded that in the adult chicken liver the embronic enzymes--glycogen phosphorylase and glycogen synthetase--are retained.     

The enzymes of adenine nucleotide metabolism in developing skeletal muscle

1. During late foetal and early post-natal development of rabbit skeletal muscle the total protein increased more rapidly than the non-protein nitrogen content per g. wet wt. 2. AMP-deaminase activity of rabbit leg muscles increased rapidly over the period 5-15 days after birth. In diaphragm muscle from the same animal the rapid increase to the adult enzymic activity took place at about the time of birth. 3. The rapid increase in AMP-deaminase activity of leg muscle occurred earlier in animals born relatively mature, such as the chick and guinea pig, than in animals less well developed at birth, such as the rabbit and rat. 4. The pattern of enzymic activity shown by AMP deaminase during development in diaphragm, leg and cardiac muscles in a given species was closely paralleled by those of adenylate kinase and creatine phosphokinase. 5. When young rabbits were encouraged to become active at an earlier stage than is normal, the rise in creatine-phosphokinase activity occurred at an earlier age than in the control animals. 6. The results suggest that the activity pattern of the muscle is an important factor in determining the time at which the activities of the enzymes of special significance for muscle rise sharply to the adult values. 7. Development in rabbit leg muscle also involved an increase in aldolase activity. The pattern of change was similar to that obtained with other enzymes studied.     

Heterogeneity of liver acid phosphatases in developing chick embryo

1. The development, localization and heterogeneity of acid phosphatase and a Zn(2+)-activated acid phosphatase in cellular fractions of developing chick liver were studied. 2. Acid phosphatase is distributed abundantly in the particulate and soluble fractions. The soluble fraction is rich in Zn(2+)-activated acid phosphatase, which attains its peak activity at about 15 days of incubation. 3. The particulate acid phosphatase activity is inhibited by fluoride but not by sodium l(+)-tartrate or cysteine. On the other hand, the soluble Zn(2+)-activated acid phosphatase activity is inhibited by sodium l(+)-tartrate and cysteine but not by fluoride. 4. The pH optimum of these two enzymes is similar at about 5.6. 5. The soluble Zn(2+)-activated acid phosphatase activity appears to be thermally stabilized by the treatment with Triton X-100 or bovine serum albumin.     

Role of polyfunctional glucose-6-phosphatase in the liver carbohydrate metabolism of the developing chick embryo

Glucose-6-phosphatase was shown to be polyfunctional in the liver of the developing chick embryo. Changes in the activity of glucose-6-phosphate phosphohydrolase did not correlate with the rate of gluconeogenesis. The activity of this enzyme increased from the 16th to the 20th day of embryogenesis. The activities of pyrophosphate-glucose phosphotransferase, carbamyl-phosphate-glucose phosphotransferase did not change during embryogenesis. The ratio of the activities of phosphohydrolase and phosphotransferases was characterized by the predominance of the phosphohydrolase activity. The values of latency of phosphohydrolase and phosphotransferases did not correlate with the rate of gluconeogenesis. Glucose-6-phosphate phosphohydrolase was found not only in the microsomal, but in the nuclear fraction as well. KM(G6P) of the enzyme of the nuclear fraction differed from KM of the microsomal enzyme.     

Vitamin D metabolism and its possible role in the developing chick embryo.

The relationship between bone formation and vitamin D metabolism was investigated in the developing chick embryo. Fertilized White Leghorn eggs were incubated at 38 degrees C in an incubator for 21 days. The fresh weight and calcium content of embryonic tibiae began to increase at day 12 and attained maximal values at day 19. Bone alkaline phosphatase and citrate decarboxylation activities, both of which represent osteoblastic activity, also began to increase at days 10-12, reached maximal values at day 19 and sharply declined thereafter. Both bone enzyme activities were highly correlated with CA2+-binding activity in the chorioallantoic membrane measured by the Chelex 100 assay. When mesonephric and metanephric homogenates were incubated with 25-hydroxy[3H]cholecalciferol, a marked and concomitant increase occurred in the metanephric 1 alpha- and 24-hydroxylase activity after day 14. The production of 1 alpha, 25-dihydroxycholecalciferol attained a maximal value at day 19 and decreased thereafter, whereas that of 24,25-dihydroxycholecalciferol continued to increase until hatching. The production rate of 1 alpha, 25-dihydroxycholecalciferol by the metanephros coincided with the changes in Ca2+-binding activity in the chorioallantoic membrane and osteoblastic activity. Since both intestinal calcium absorption and bone mineral mobilization do not occur in embryonic life, these results support the idea that 1 alpha, 25-dihydroxycholecalciferol may be involved directly in bone formation or induction of a calcium-binding protein in the chorioallantoic membrane.     

Enzymes of purine metabolism in the nuchal muscle (M. complexus) of chick embryo]

The developmental patterns of enzyme activities related to GMP metabolism have been investigated in chick embryo musculus complexus (m. Complexus). Guanylate phosphatase activity increases conspicuously from 18th to 21st day, guanosine phosphorylase increases on the 21st day and the guanase shows a very low activity during the whole period considered. Xanthine oxidase was always found absent. The results suggest that during the first period of incubation GMP breakdown in chick embryo m. complexus might follow a catabolic pathway, while starting from the 18th day some guanine might be converted to GMP originating a new metabolic pathway as previously suggested for AMP metabolism.     

Erythropoiesis in the developing chick embryo

The types of erythroid cells of chick embryos developing in ovo have been correlated with the hemoglobins of the embryos. Prior to 5 days, when primitive cells constitute the only erythroid cells, two hemoglobins can be resolved by polyacrylamide gel electrophoresis. The two adult hemoglobins and a minor hemoglobin found only in embryos and young chicks first appear simultaneously with initiation of definitive erythropoiesis.     

Koelliker haemoglobins in developing chick embryo

1. Three Koelliker haemoglobins, HbKE, HbKA and HbKH, derived from a post-translational loss of alpha-Arg-141, were isolated from red cells of chicken embryos. HbKE is typical of embryos up to 7 days of incubation, HbKA and HbKH are found in mature embryos. 2. All the precursor haemoglobins contain alpha A chains. HbKA derives from adult haemoglobin A whose globin composition is alpha A2 beta 2, HbKH from embryonic haemoglobin H with a globin composition alpha A2 beta H2 and HbKE from embryonic haemoglobin E with globin composition alpha A2 epsilon 2. 3. No Koelliker derivatives of haemoglobins with alpha-like chains other than alpha A were observed.     

Glycogen metabolism in the prelaid chick embryo.

Glycogen metabolism has been studied during the development of the early chick embryo, at the cytochemical and ultrastructural levels. Two waves of glycogen synthesis and breakdown have been found. In the first, free clusters of glycogen particles are synthesized at late oogenesis. These clusters are found later in invaginations of the membrane of vesicles containing a floccular material (FLOV). The glycogen clusters are degraded there during ovulation and the first hours in the oviduct. The second wave of glycogen synthesis begins before cleavage, reaching a maximum at mid-uterine age. This second wave occurs in another type of vesicle (GLYV), which eventually disintegrates releasing free clusters of glycogen granules. This glycogen is degraded in membranous structures containing a floccular material, as in the first wave of degradation. The degradation ends at the late uterine stages, and at the same time numerous ribosomes are formed. This period corresponds to area pellucida formation, which probably depends on the energy liberated during the second wave of glycogen degradation.