Chemical modification with 2,3-butanedione in borate buffer indicates that nine of ten glycolytic enzymes studied contain arginyl residues at their active sites. Fructose-1,6-diphosphatase also has arginines at its binding site for the allosteric inhibitor, adenosine monophosphate. These and other data suggest that, as a general rule, enzymes acting on anionic substrates or cofactors will probably contain arginyl residues as components of their ligand binding sites. This could account in part for the relatively infrequent occurrence of arginine in proteins.

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We examined the relationship of labor pain relief medications with neonatal suckling and breastfeeding duration in 129 mothers delivering vaginally. Suckling was measured using the Infant Breastfeeding Assessment Tool (IBFAT). Controlling for infant age, birthweight, and gender, infants of unmedicated mothers had higher IBFAT suckling scores than those of medicated mothers (x = 11.1 vs. x = 8.2 respectively, P = .001). IBFAT suckling scores for intravenous and epidural groups were similar (x = 8.5) while those who received a combination of both intravenous and epidural medications were lower (x = 6.4 +/- 2.96, P = .001). Mothers evaluated their breastfeeding similarly to nurse evaluators (Z = 9.39, P = .001). Breastfeeding duration did not differ between unmedicated and medicated groups; however, dyads with low IBFAT scores weaned earlier than those with medium or high scores. Labor pain relief medications diminish early suckling but are not associated with duration of breastfeeding through 6 weeks postpartum.