Postsynthetic deamidation of hemoglobin Providence (beta 82 Lys replaced by Asn, Asp) and its effect on oxygen transport

Carriers of hemoglobin Providence have three types of beta chain in their hemolysates. The two abnormal chains have asparagine (Providence N, Prov N) or aspartic acid (Providence D) at position beta 82, instead of lysine. In vitro, only two beta chains are synthesized by reticulocytes of carriers, betaA and betaProv N. In vivo studies showed that the specific activity of Providence N was initially 10-fold higher than that of Providence D; the specific activities of the two labeled hemoglobins were approximately equal 5 wk after injection of isotope. Oxygen affinity of carriers' blood was somewhat increased, but they were not polycythemic. The affinity of the purified hemoglobins Providence was decreased. Addition of 2, 3 diphosphoglycerate had little effect on the affinity of either hemoglobin component, and addition of inositol hexaphosphate produced no change in the affinity of Providence D. These studies demonstrate that Providence N is deamidated to Providence D during the life span of the erythrocyte, and suggest this finding may represent only an easily observed prototype of posttranslational modification of proteins in general. Despite and abnormal P50 of the blood, oxygen transport is probably normal in carriers of the abnormal hemoglobins.

Hemoglobin providence. Functional consequences of two alterations of the 2,3-diphosphoglycerate binding site at position beta 82

Position beta 82 in human hemoglobin (Hb) is normally occupied by lysine, a positively charged residue that is involved in the binding of anionic cofactors. This residue is substituted by a neutral residue in Hb Providence Asn and by a negatively charged residue in Hb Providence Asp. Hb Providence Asp shows more differences from Hb A than does Hb Providence Asn in studies of the kinetics and equilibria of ligand binding. For both forms, homotropic (cooperative) interactions are normal with n values of 2.5 to 2.7, while heterotropic (pH and anion) interactions are reduced greatly. The reduction in anion sensitivity is attributed to the absence of a positive residue at position beta 82. Reduction in pH sensitivity may be due to a ligand-linked change in the pK of a neighboring residue, beta 143 histidine, which normally is not a Bohr group. This change in pK would act in opposition to the normal Bohr effect. Reduction in the net positive charge of the central cavity has a further consequence. Relative to Hb A, both Hb Providence Asn and Hb Providence Asp show decreased oxygen affinities at neutral pH in the absence of cofactors. This suggests that in Hb A the binding of anionic cofactors directly influences the oxygen affinity by neutralizing the charged groups of the diphosphoglycerate binding site and thus stabilizing the low affinity (T) conformation. From pH 6 to 9 in the presence of 1 M NaCl, where all the charged groups may be masked, the oxygen-binding properties of Hb A and the Hb Providence mutants are identical. Moreover, subunit dissociation of the liganded Hb Providence mutants appears to be increased, as is known to occur for Hb A in the presence of high salt. The results obtained with Hb Providence Asn and Hb Providence Asp illustrate how single amino acid substitutions can modify hemoglobins' pH and anion interactions without altering cooperative interactions between subunits. The alteration in cofactor effects observed with these mutants also illustrates differences between the allosteric effects induced by organic and inorganic anions.

Correlation between diffuse EEG abnormalities and cerebral atrophy in senile dementia

Thirty-five elderly patients were investigated because of clinical signs of dementia. The presence or diffuse cerebral atrophy, and its severity, were determined by the use of computed tomography (CT scan). All of the patients were also examined by electroencephalography (EEG), and the presence of diffuse abnormalities, especially diffuse slowing, was noted. Specifically, patients with normal or near-normal EEGs were compared with those with severe diffuse slowing. No correlation between the presence or severity of diffuse EEG abnormalities and the degree of cerebral atrophy as measured by CT scan was found. Though the EEG is clearly identifying physiological dysfunction of nerve cells in demented patients it does not appear to be reliable tool for the prediction of diffuse cerebral atrophy in this population.

Biosynthesis of bacterial glycogen. Purification and properties of the Escherichia coli B ADPglucose:1,4-alpha-D-glucan 4-alpha-glucosyltransferase

The Escherichia coli B glycogen synthase has been purified to apparent homogeneity with the use of a 4-aminobutyl-Sepharose column. Two fractions of the enzyme were obtained: glycogen synthase I with a specific activity of 380 mumol mg-1 and devoid of branching enzyme activity and glycogen synthase II having a specific activity of 505 mumol mg-1 and containing branching enzyme activity which was 0.1% of the activity observed for the glycogen synthase. Only one protein band was found in disc gel electrophoresis for each glycogen synthase fraction and they were coincident with glycogen synthase activity. One major protein band and one very faint protein band which hardly moved into the gel were observed in sodium dodecyl sulfate gel electrophoresis of the glycogen synthase fractions. The subunit molecular weight of the major protein band in sodium dodecyl sulfate gel electrophoresis of both glycogen synthase fractions was determined to be 49 000 +/- 2 000. The molecular weights of the native enzymes were determined by sucrose density gradient ultracentrifugation. Glycogen synthase I had a molecular weight of 93 000 while glycogen synthase II had a molecular weight of 200 000. On standing at 4 degrees C or at -85 degrees C both enzymes transform into species having molecular weights of 98 000, 135 000, and 185 000. Thus active forms of the E. coli B glycogen synthase can exist as dimers, trimers, and tetramers of the subunit. The enzyme was shown to catalyze transfer of glucose from ADPglucose to maltose and to higher oligosaccharides of the maltodextrin series but not to glucose. 1,5-Gluconolactone was shown to be a potent inhibitor of the glycogen synthase reaction. The glycogen synthase reaction was shown to be reversible. Formation of labeled ADPglucose occurred from either [14C]ADP or [14C]glycogen. The ratio of ADP to ADPglucose at equilibrium at 37 degrees C was determined and was found to vary threefold in the pH range of 5.27-6.82. From these data the ratio of ADP2- to ADPglucose at equilibrium was determined to be 45.8 +/- 4.5. Assuming that deltaF degrees of the hydrolysis of the alpha-1,4-glucosidic linkage is -4.0 kcal the deltaF degrees of hydrolysis of the glucosidic linkage in ADPglucose is -6.3 kcal.

The validity of criteria for the evaluation of cerebral atrophy by computed tomography

Computed tomography of the brain was used in evaluating demented and nondemented elderly people. The incidence of convulutional atrophy and ventricular enlargement correlated well with pathologic and pneumoencephalographic examination of a similar population. Computed tomography also showed certain instances of dementia without atrophy and evidence of atrophy without dementia. The absence of brain atrophy in a demented patient should prompt a search for a potentially treatable cause of the dementia. The authors discuss criteria for diagnosing atrophy by computed tomography and conclude that, because of its noninvasive nature, it is a valuable aid in screening demented patients for treatable diseases.

The use of structural diagnostics in recognition

The suggestion of Krueger (1973) and other that wholistic processes underlie certain perceptual judgments is taken up in this paper. It is argued that properties such as bilateral symmetry can have a "diagnostic" significance for visual matching tasks. Diagnosticity means that if the property is present the appropriate response to a stimulus could theoretically be determined without any other analysis of the stimulus. Experiments 1 and 2 indicate that symmetry is exploited as a diagnostic property for the simultaneous same-different judgment. Displays that show the diagnostic form produce short reaction times. These experiments also show that the diagnosticity effect can be demonstrated independent of potentially confounding factors such as simplicity or redundancy. Experiments 3, 4, and 5 discount further confounding factors and also show that other properties, notably parallelism and colinearity of stimulus elements, can also be exploited as diagnostic in the simultaneous matching task. Diagnostics can have a structural or relational form. Diagnostic features are viewed as two-place structural predicates. Whether these diagnostics always have the same underlying form or not, the need for some representation of structure is a prerequisite for understanding even these simple recognition phenomena.

Recognition and attention

Sternberg has suggested that a possible way of achieving identification of degraded stimuli would be to execute “preprocessing” operations prior to recognition. Such operations would have some parallels with the “filtering” operations, suggested by Broadbent and others, for perceptual selection and attention. But when trying, in this paper, to consider how such operations could be implemented, some rather non-trivial problems emerge. Experimentally, these doubts find support in visual selection tasks of quite general character, in that filtering does not appear to take place. It seems, however, that these problems may be successfully overcome by some simple, though implicative, conceptual changes. The main implication is that effective focal attention is rather likely to be achieved through a process that is best described as “context-sensitive” selection.

Biological availability of digoxin from Lanoxin produced in the United Kingdom

Though established quality control standards were maintained, the bioavailability of digoxin from Lanoxin tablets produced in the United Kingdom fell in 1969, and was restored in 1972. After 1.5 mg doses of representative batches, tablets made between 1969 and 1972 produced mean values for area under the 50 hours plasma concentration/time curve of 36.6 ng/ml/hr and four-day urinary excretion of 340 mug, compared with respective values of 67.5 ng/ml/hr and 696 mug for recently produced tablets.After 0.5 mg doses of four recent independently produced batches of Lanoxin tablets no significant between-batch difference was found for area under the plasma concentration/time curve or cumulative urinary excretion.Absorption of digoxin from batches of Lanoxin manufactured since May 1972 is uniform and consistent. Content uniformity is an inadequate measure of tablet quality, and consistent digoxin bioavailability cannot be ensured by existing regulations.

Predicting rehospitalization from community placement

120 patients were given the Minnesota Multiphasic Personality Inventory (MMPI) prior to placement in family care and in board and care homes. After 1 yr., 20 patients had been rehospitalized. Another group of 20 patients was randomly selected from those who had not been rehospitalized during the year. The 2 groups were compared on various MMPI scales and with respect to age, sex, length of hospitalization, and type of placement to which they were sent. Type of placement was a significant factor in length of patient community residence.