Influence of steric factors on oxygen binding. I. Studies on 2,4-diisopropyldeuteroheme-myoglobin.

Sperm whale apomyoglobin was recombined with 2,4-diisopropyldeuterohemin to form 2,4-diisopropyldeuteroheme-myoglobin and its various physico-chemical properties were investigated to get an insight into the structural and functional role of the peripheral vinyl groups. 2,4-Diisopropyldeuteroheme-myoglobin showed a four times lower oxygen affinity at 25 degrees C and larger enthalpy and entropy changes of oxygenation than the corresponding values of native myoglobin. 2,4-Diisopropyldeuteroheme-metmyoglobin shows a pKa value of 9.68 which is higher than those of native metmyoglobin and mesoheme-metmyoglobin. The rate of autooxidation of oxy-form was about seven times larger in 2,4-diisopropyldeuteroheme-myoglobin than in native myoglobin. The electron-donating effect of isopropyl groups does not give straightforward explanation for these anomalous properties of 2,4-diisopropyldeuteroheme-myoglobin. It is proposed that site and stereospecific van der Waals' interaction between the polypeptide side chains and the peripheral 2,4-diisopropyl groups may weaken the interaction between the bound oxygen molecule and the distal His, resulting in the decrease in the stability of oxyform.     

Symposium on diarrhea. 3. Investigation of chronic diarrhea.

The practical approach to the investigation of diarrhea must be logical and based on anatomic considerations. The site of the underlying disorder may be determined by the clinical picture, and the logic of investigation will be influenced by the history. Important specific investigation in a case of colonic diarrhea include a careful rectal examination, stool inspection, sigmoidoscopy, rectal biopsy and barium enema study. Colonoscopy has been used, but its role has yet to be defined. In a case of small-bowel steatorrhea or diarrhea quantitative chemical estimation of the daily output of stool fat is useful, and to this investigation is added a small-bowel radiograph series and, if the radiographic findings are abnormal, small-bowel biopsy. Other investigations for small-bowel disease may include the breath test with carbon-14-labelled glycocholic acid, the lactose tolerance test, duodenal aspiration for giardiasis, analysis of serum immunoglobulins and, on occasion, isolation of vasoactive intestinal polypeptide hormone (which may aid the diagnosis of functioning tumours of the pancreas or small bowel). Investigations for pancreatic steatorrhea include abdominal radiography, performance of the secretin test and testing of the response to pancreatic replacement therapy. In some patients it may be useful to use endoscopic retrograde cholangiopancreatography to differentiate pancreatic carcinoma and chronic pancreatitis.     

Studies on the control of antibody synthesis. IX. Effect of boosting on antibody affinity.

The effect of boosting on antibody affinity was studied in a haptenic system. Generally, boosting results in the prompt synthesis of high affinity anti-hapten antibody. However, repeated boosting frequently leads to a decrease in the amount and affinity of the serum antibody. Repeated boosting with hapten on a carrier different from that used for priming selectively stimulates synthesis of the highest affinity anti-hapten antibody and does not result in a decrease in affinity. Priming with soluble antigen without adjuvants results in the synthesis of low affinity antibody. After such priming, boosting stimulates low affinity antibody synthesis and repeated boosting leads to a moderate increase in antibody affinity.