The physics of lipid bilayers, a model system for biological membranes, has been studied for varying lipid and protein constituents. The effects of molecules that transiently associate with the bilayer is a new area of research. These membrane-associated molecules have been implicated in multiple processes necessary for proper cell function. In this work, we focus on two proteins involved in vesicle trafficking inside cells, Arf1 and ArfGAP1. Research has suggested that these proteins may act as curvature generators or curvature stabilizers. We generalize this hypothesis to suggest that the addition of these proteins to unilamellar vesicles would alter the physical characteristics of the lipid bilayers to favor deformations that lead to vesicle formation. While results from measurements of global properties such as membrane surface tension and bending rigidity are inconclusive due to the large variability intrinsic to vesicle samples, we find that the addition of peptide alters the thermally driven fluctuations of the vesicles and biases the membrane shape during local deformations of the vesicle. Fluorescent probe experiments indicate that the association of myristoylated Arf1 peptide increases the packing of lipid molecules in the membrane. This work points to a potential novel role for these proteins as suppressors of negative curvature and calls for refinement of traditional techniques used to measure the physical properties of vesicles.