Methylation Of Carboxyl Groups Research Articles

Enzymic synthesis of loganin by carboxyl group methylation of loganic acid

We have found that mevalonic acid-2-“C is incorporated into the aglucone moiety of the iridoid glucoside, loganic acid (fig. l), in both flowering JGzcu rosea and germinating seedlings [ I] . Loganin, its methyl ester, serves as a precursor of the nontryptophan moiety of three different classes of indole alkaloids in the same plant [2,3]. However, the occurrence of 7deoxyloganin in V. roseu has also been reported and this glucoside was found to be hydroxylated to loganin in vivb. Since tracer studies in a related species, Menyanthes tn’foliata, have revealed that the O-methyl group of loganin is derived from the methyl of methionine [4] , it was of interest to determine which monoterpene, loganic acid or 7-deoxyloganic acid, is methylated prefentially in Y rosea.

Physicochemical studies of ultraviolet-irradiated bovine serum albumins

Experiments performed with bovine serum albumin (BSA) and its modified derivatives over a wide pH range, have shown the lack of correlation between the aggregation und absorbancy increase effects produced by ultraviolet (UV) irradiation. The aggregation effect was found to be governed mainly by the over-all charge on BSA or its derivatives with the exception of iodinated BSA which showed marked resistance to aggregation over the entire pH range. The influence of over-all protein charge on the aggregation effect produced by UV irradiation was further confirmed by studies with BSA-detergent complexes. Prior addition of Zephiran enhanced, sodium dodecyl sulfate and caprylate inhibited, and Tweeu 80 was without effect with regard to aggregate formation with UV light. Modification of tyrosyl side chains, e.g., iodinated or diazotized BSA, changed the UV absorbancy increase pattern of BSA in the acidic pH range at wavelengths <3000 A. Modification of the amino group, e.g., acetylated or guanidylated BSA, changed the absorbancv increase pattern of BSA in the alkaline range usually at wavelengths above 3000 A. Methylation of carboxyl groups (McBSA) produced little or no change in the UV absorbancy increase spectra. Changes in the absorbancy increase may be attributed either to modification of the tyrosyl side chains or to changes in hydrogen bonding between amino find tyrosyl groups.