Reaction of formaldehyde with the histidine residues of proteins

Imidazoles or imidazoles substituted in the 2 or 4(5) position but with the ring nitrogen free, give a positive Pauly reaction. N-Methylimidazole does not react. In the presence of formaldehyde, all imidazole compounds give a negative Pauly reaction. In agreement with nmr studies, it is concluded that formaldehyde reacts with the imidazole ring nitrogen in acid solution to form N-hydroxymethyl derivatives.The Pauly color yield of various proteins (chymotrypsin, TPCK-chymotrypsin, lysozyme, ribonuclease, and reduced ribonuclease) is reduced 90–95% when the reaction is performed in the presence of formaldehyde. The color yield in water is essentially accounted for by the known reactive histidine and tyrosine content. In the presence of formaldehyde the color yield can be interpreted as arising from the known tyrosine content. It is therefore concluded that the histidine residues of the proteins examined have reacted with formaldehyde to form N-hydroxymethyl derivatives.In contrast to the Pauly color yield of chymotrypsin (A_M, 52 720) which can be accounted for by the contribution of its two histidine and three reactive tyrosine residues, the color yield of TPCK-chymotrypsin (A_M, 47 685) is higher than would be expected on the basis of the reported site of reaction of TPCK with chymotrypsin. The experimental molar extinction coefficient should be close to that calculated (A_M, 31 300) for its presumed one reactive histidine and three tyrosine residues. That it is not is in agreement with a previous report from our laboratories suggesting that His-57 is not the only site of reaction of TPCK with chymotrypsin.     

p-Hydroxybenzaldehyde as a major constituent of the epicuticular wax of seedling Sorghum bicolor

p-Hydroxybenzaldehyde is present in concentrations up to 30% in the wax of Sorghum bicolor seedlings. It is highly deterrent to locusts, reducing their normal feeding by 90%.     

A case of acute myelomonocytic leukaemia associated with therapy: Feulgen-DNA microdensitometric determinations.

A cytochemical study of a case of acute myelomonocytic leukaemia, which arose after radiation therapy and polychemotherapy for Hodgkin's disease, is presented. The distribution of the DNA content of the circulating blood cells appears to be different from the unimodal diploid distribution reported in the literature for acute myelomonocytic leukamias not associated with therapy. This finding seems to strengthen the hypothesis, already put forward by Marinone et al. (1979), that a particular pattern of DNA content distribution could be characteristic of leukaemias linked to chemotherapy and radiotherapy.